Washington: Israel's decision to attack Syria on September 6, bombing a suspected nuclear site set up in apparent collaboration with North Korea, came after Israel shared intelligence with US President George W. Bush this summer indicating that North Korean nuclear personnel were in Syria, US government sources said.

The Bush administration has not commented on the Israeli raid or the underlying intelligence. Although the administration was deeply troubled by the Israeli assertion that North Korea was assisting the nuclear ambitions of a country closely linked with Iran, sources said, the White House opted against an immediate response because of concerns it would undermine long-running negotiations aimed at convincing North Korea to abandon its nuclear programme.

Ultimately, however, the United States is believed to have provided Israel with some corroboration of the original intelligence before Israel proceeded with the raid, which hit the Syrian facility in the dead of night to minimise possible casualties, the sources said. The target of Israel's attack was said to be located in northern Syria, near the Turkish border. A Middle East expert who interviewed one of the pilots involved said they operated under such strict operational security that the airmen flying air cover for the attack aircraft did not know details of the mission. The pilots who conducted the attack were briefed only after they were in the air, he said. Syrian authorities said there were no casualties.

US sources would only discuss the Israeli intelligence, which included satellite imagery, on condition of anonymity, and many details about the North Korean-Syrian connection remain unknown. The quality of the Israeli intelligence, the extent of North Korean assistance and the seriousness of the Syrian effort are uncertain, raising the possibility that North Korea was merely unloading items it no longer needed. Syria has actively pursued chemical weapons in the past, but not nuclear arms - leaving some proliferation experts sceptical of the intelligence that prompted the Israeli attack.

Syria and North Korea last week both denied they were cooperating on a nuclear programme. President Bush refused to comment on Israel's attack on Thursday, but he issued a blunt warning to North Korea that 'the exportation of information and/or materials' would affect negotiations under which North Korea would give up its nuclear programmes in exchange for energy aid and diplomatic recognition.

"To the extent that they are proliferating, we expect them to stop that proliferation, if they want the six-party talks to be successful," he said at a news conference, referring to the negotiations that also include China, Japan, South Korea and Russia.

Unlike Israel's destruction of an Iraqi nuclear reactor in 1981, Israel made no announcement of the recent raid and imposed strict censorship on reporting by the Israeli media. Syria made only muted protests, and Arab leaders have remained silent.

Crucial strike

"There is no question it was a major raid. It was an extremely important target," said Bruce Riedel, a former intelligence officer at Brookings Institution's Saban Centre. "It came at a time the Israelis were very concerned about war with Syria and wanted to dampen down the prospects of war. The decision was taken despite their concerns it could produce a war. That decision reflects how important this target was to Israeli military planners."

Israel has long known about Syria's interest in chemical and even biological weapons, but "if Syria decided to go beyond that, Israel would think that was a real red line," Riedel said.

Edward Djerejian, a former US ambassador to Syria and founding director of Rice University's Baker Institute, said that when he was in Israel this summer he noticed "a great deal of concern in official Israeli circles about the situation in the north," in particularly whether Syria's young ruler, Bashar Al Assad, "had the same sensitivity to red lines that his father had." Bashar succeeded his father Hafez Al Assad as president of Syria in 2000.

The Israeli attack came just three days after a North Korean ship docked at the Syrian port of Tartus, carrying a cargo that was officially listed as cement. The ship's role remains obscure. Israeli sources have suggested it carried nuclear equipment, others have claimed it contained only missile parts, and some have said the ship's arrival and the attack are merely coincidental. One source suggested that Israel's attack was actually prompted by a fear of press leaks on the intelligence.