Hamas and other terrorist organizations in the Gaza Strip have used the newly open border with Egypt to send numerous terrorists into the Sinai peninsula over the last two days, with the goal of then sending them from Sinai into Israel to commit attacks, defense officials said yesterday.

The Israel Defense Forces, the police and the Shin Bet security service have consequently beefed up their forces and their alert level along the Israeli-Egyptian border in an effort to thwart infiltrations. Should terrorists succeed in entering Israel from Sinai, one defense official said, they might commit suicide bombings, kidnap soldiers or civilians or attack small agricultural communities or military outposts.

In addition, the counterterrorism unit in the Prime Minister's Office warned Israelis against visiting Sinai and urged those who are already there to leave, since the flow of terrorists from Gaza also increases the likelihood of terror attacks in Sinai's tourist resorts. Egypt is also worried about the possibility of terror attacks in Sinai.

One member of the counterterrorism unit noted that the open border not only enables terrorists to enter Sinai, but would also make it easier for them to smuggle an abducted Israeli back into Gaza.

Due to fear of a terrorist infiltration, the IDF yesterday shut down Route 10, which runs along the Egyptian border. The army said it also briefed southern communities on the situation and asked the Education Ministry to ban school trips in certain parts of the Negev and Arava.

Defense officials said the terrorists in Sinai are most likely to try to strike immediately, and almost certainly within the next two weeks. The Shin Bet currently has 11 active terror warnings, most involving Gaza terrorists who moved into Sinai; only a few are from the West Bank. The police, which define the term more broadly, count 15 terror warnings.

Public Security Minister Avi Dichter told the police brass yesterday that there is "a danger of terrorists trying to enter Israel [from Sinai] along with infiltrators from Africa," referring to refugees and economic migrants. The terrorists might also first send a band of ordinary smugglers into Israel to test the defense forces' preparedness.

The defense establishment believes that the most extremist Hamas leaders in Gaza - such as former foreign minister Mahmoud a-Zahar and the heads of the organization's military wing, Ahmed Jabari and Mohammed Def - are in any case interested in carrying out spectacular attacks to make up for Hamas's failures in battles with IDF forces in Gaza in recent weeks. But the open border, by making it easier to send terrorists from Gaza into Sinai and thence to Israel, is likely to accelerate the timetable.

According to defense officials, the events of the past week were a huge victory for Hamas, which succeeded in dictating the agenda to Israel.

IDF officers pointed out this week that Israel continues to finance the salaries of Palestinian government employees in offices controlled by Hamas: It transfers tens of millions of shekels a month to the Palestinian Authority, which uses the money to pay salaries in both the West Bank and Gaza. The IDF believes that this has enabled Hamas to divert funds to building up its military capabilities.

Barak Ravid and Yuval Azoulay contributed to this report.