An Israel Defense Forces inquiry committee, headed by Major General Meir Kalifi, is examining two main options for what caused an IDF shell to stray 500 meters off course to the northern Gaza Strip town of Beit Hanun, killing 19 Palestinians, mostly women and children.

The committee believes that the disaster was the result of either a technical problem or human error. The problem (or error) could have occurred in either the artillery battery's radar or its firing computer, both of which are operated manually.

The panel is due to submit its findings to Defense Minister Amir Peretz and IDF Chief of Staff Dan Halutz by Thursday night. Soon after the attack, Peretz ordered the IDF to freeze all artillery shelling of Gaza until the investigation had been completed.

Based on the committee's findings to date, the course of events leading up to the incident is as follows:

At 4 P.M. on Tuesday, four new and improved Qassam rockets were fired at Ashkelon from a copse north of Beit Hanun. No one was hurt.

Later that evening, the IDF obtained intelligence indicating that Hamas intended to fire more of the new-model Qassams at Ashkelon Wednesday morning, apparently from the same site - which was chosen because it is not visible from any IDF lookout post.

The Gaza Division - which has in general sharply reduced its use of artillery fire since Brigadier General Moshe Tamir took command of it in August - therefore instructed the artillery battery stationed at Be'eri to be prepared to shell the site, in the hope that this would deter the Qassam launchers from going there.

The battery then made the usual preparations to adjust the range: It fired three or four shells at a site a few hundred meters away from the real target and used the battery's radar to find out where they had landed, after which it adjusted the guns' settings accordingly.

At about 5:30 A.M. Wednesday morning, the battery fired 12 shells programmed to land about 1,200 meters from the houses of Beit Hanun. These shells hit the target and caused no casualties.

At 5:45 A.M., the battery fired another 12 shells, this time programmed to land about 450 meters from the houses. All were launched from a single barrel to increase the accuracy. According to the battery's radar, 10 shells hit the target, but the radar was unable to determine where the other two had landed. A few minutes later, the first reports of civilian casualties in Beit Hanun began arriving.

Unknown number of shells The IDF is still not sure whether only the missing two shells hit the al-Ottomana house, or whether there were more. Artillery gunners who saw photographs of the damage on television said it looked as if a sizable number of shells had landed on it.

According to the IDF, the "normal" margin of error for an artillery shell under these conditions is about 200 meters, which is why IDF regulations for Gaza state that artillery targets must be at least 200 to 300 meters from civilian houses. But a 450-meter deviation would require only a three-degree deviation in the gun barrel, which is "undetectable by the human eye," said Brigadier General (reserves) Zvi Fogel, a former senior artillery officer.

Fogel told Haaretz that there are two possible explanations for the error: a problem with the radar, which resulted in the gun's range being wrongly adjusted Tuesday evening, or a problem with the battery's computer, which wrongly implemented the correct range settings obtained from the radar.

Kalifi, who is heading the inquiry committee, also presided over the IDF's probe of a blast that killed several members of a Palestinian family on a beach near Beit Lahia last June. In that inquiry, Kalifi concluded that the blast was caused not by an IDF artillery shell, but by Hamas explosives planted near the site to foil a possible landing by naval commandos. The Palestinians completely rejected this conclusion.

In this case, however, IDF officers said there was no doubt that IDF shells were responsible; the only question is how the error happened.

IDF officer: Shells were aimed 500 meters from where they hit An initial Israel Defense Forces investigation has found that the artillery shells that killed 19 Palestinians in northern Gaza on Wendesday were "aimed 500 meters away from where [they] hit," IDF GOC Southern Command Yoav Galant told Channel 2.

"Our estimate is that it was something connected with the aiming devices, or the alignment, or the balance between them, or our radar's location of the shell hit ... Our investigation is concentrating on these points," he said.

Still, Galant defended the shelling, saying: "Israel's citizens don't know how many times artillery fire has prevented Qassam [rocket] launches. When you fire at the launching area area two or three hours in advance, there is a good chance of preventing the Qassam fire."

Prime Minister Ehud Olmert and Defense Minister Peretz on Wednesday expressed regret over the Gaza deaths, and Peretz called for a cease in shelling pending the results of the probe.

"The defense minister has ordered a stop to the firing of artillery into Gaza until an investigation into the incident is finished," a Defense Ministry spokeswoman said.

At least 50 people were wounded on Wednesday when artillery fire struck a residential area in the town of Beit Hanun. Eight children and four women were among the dead. Olmert and Peretz also offered emergency humanitarian assistance and medical care for those wounded in the attack.

According to Army Radio, Peretz has instructed Major General Yosef Mishlav, the government coordinator for the territories, to provide emergency humanitarian support for Palestinians hurt in the shelling.

Peretz also decided to open the Rafah crossing for two days in order to ease conditions for Gaza residents, Army Radio reported.

Foreign Minister Tzipi Livni expressed regret over the incident, saying: "Israel left Gaza in order to give the Palestinians an opportunity to control terrorism and develop their own lives. Unfortunately, this has not happened."

"Israel is faced with constant attack by the Palestinian terror organizations, in the form of relentless firing of Qassam rockets at Israeli population centres," she told a joint news conference with her Norwegian counterpart Jonas Gahr Stoere in Tel Aviv.

"Israel has no desire to harm innocent people, but only to defend its citizens. Unfortunately, in the course of battle, regrettable incidents such as that which occurred this morning do happen."

Government spokeswoman Miri Eisen also expressed regret for the deaths, telling CNN that Israel did not deliberately target civilians.

Responding to the Beit Hanun attack, Kadima MK Otniel Schneller pointed to the continued Qassam rocket fire as the direct cause of the incident. According to Schneller, Israel should not apologize for defending its citizens against terror attacks.

Uri Ariel (NRP-National Union) said he believes terror organizations in Gaza are not just killing Israelis. According to Ariel, those who know the terror organizations' mode of operation understand that they are operating from within civilian areas.

Likud MK Yuval Steinitz said that despite the great sorrow over the deaths of innocent civilians, the responsibility lies entirely with the terror organizations, which use residents of Beit Hanun as human shields for the launching of Qassam rockets on Sderot.

Arab, leftist MKs slam shelling Arabs MKs responded harshly Wednesday to the incident, with Deputy Knesset Speaker Ahmed Tibi (Ra'am-Ta'al) calling on Defense Minister Amir Peretz to resign.

Tibi said that under Peretz, the IDF had committed war crimes, and demanded that the defense minister be called to account in the Knesset for "the massacre." He also called for an independent commission of inquiry into the shelling.

The chairman of Ra'am-Ta'al, Sheikh Ibrahim Tsartsur, slammed the Olmert government as a "bloody government is not interested in peace." He said that "Israel bears full responsibility for the events" in Gaza.

MK Mohammed Barakeh of Hadash condemned the "war crimes and massacre in Beit Hanun."

"The sight of the martyrs of the massacre is testament to the cruelty of Israel, which continually seeks more wars, crimes and massacres," he said.

Meretz Chairman Yossi Beilin said the moral and diplomatic price Israel will pay as a result of the strike is much greater than any achievement that could have been gained by such an attack. Beilin called on the government to immediately halt all military activity and begin intensive negotiations on a full ceasefire.

Meretz faction whip Zahava Gal-On also criticized the action, and said the government is trapped in a cycle of violence in Gaza from which it has not plans to extricate itself. Gal-On said the government's mentality makes it impossible to bring quiet to Sderot.

Labor MK Nadia Hilou said Israel had "awakened to a black morning," adding "Once again innocent civilians and children are paying with their lives. Our leaders must wake up."