Two people died on Tuesday evening and another person died of his wounds on Wednesday after a leak at a Haifa oil refinery released a cloud of toxic gas.

Following the leak, Israel's rescue service said four people were in critical condition after inhaling poisonous material. Two later died in the hospital, and the third died early Wednesday morning.

The first two victims were identified as cousins George Zaatrah, 31, and Tamer Marjiah, 33, and the third was Tamer al Haj, 18, all from the village of Yafia near Nazareth.

"We arrived at the scene to find four people unconscious, two of whom had to be brought down from a height of several meters from the installation where they had been working," paramedic Eli Geller told Haaretz.

The four were not breathing and had no pulse when they were found, Geller said. He added that one's pulse has been restored, while a second was showing signs of recovery.

Seven others, all refinery employees, were in stable condition and two paramedics also received treatment.

The cause and source of the leak were not immediately known.and it was not certain what type of gas had escaped.

Oil Refineries Ltd, the owner of the site, said in a statement:

"Refinery installations have been shut down over the last month for scheduled work. As part of this, a number of workers approached an installations containing gas, wearing full protective gear, including masks. For a reason that is not yet clear, they were affected by the flow of gas."

According to the Shlomo Katz, the Haifa district manager in the Ministry of Environment, the incident was a work accident caused by negligence.

"It is clear that this was a specific event that couldn't have been caused by anything other than negligence," Katz said. "They did not work according to protocols. If they would have worked as they were asked with a closed security system this never would have happened."

Katz added that the toxic gases that hurt the employees were a mixture of toxic substances, among them Hydrogen sulfide (H2S).

The huge oil refinery in Haifa, one of Israel's largest cities, has been a target of environmentalists and worried residents because of the potential for widespread damage and casualties in the event of an accident or an attack.

During a 34-day war with Lebanese Hezbollah guerrillas in 2006, a Katyusha rocket fired from south Lebanon hit an open area in the facility, causing minor damage, according to the refinery company.