Officials said North Korea has provided nuclear material and guidance to Syria. They said Pyongyang has helped establish underground facilities that could be used to produce weapons-grade uranium for the regime of Syrian President Bashar Assad.

"There are indicators that they do have something going on there," Semmel, who did not rule out the involvement of the so-called nuclear smuggling network once led by Abdul Qadeer Khan, said on Sept. 13.

Officials said North Korean ships arrived in Syria in mid-2007 with cargo suspected to have included weapons of mass destruction components. They said both Israel and the United States have been tracking these shipments, which in some cases were registered as cement.

[On Sunday, Iran said Russia was ready to ship enriched uranium fuel for the Bushehr nuclear energy reactor. Iranian Foreign Minister Manouchehr Mottaki said the nuclear fuel for Bushehr was inspected and sealed by the International Atomic Energy Agency.]

"There are North Korean people there," Semmel said. "There's no question about that. Just as there are a lot of North Koreans in Iraq and Iran."

Israel has not denied an air force operation in Syria. But officials have refused to provide any details.

For its part, Syria has insisted that Israeli fighter-jets did not stage an attack. On Monday, Syrian sources told the London-based A-Sharq Al Awsat daily that the Israeli operation was meant to test Syrian air defense systems.

But Western intelligence sources said the Israeli strike, termed Operation Orchard, consisted of eight aircraft, at least two of them F-15I fighter-jets, four F-16Is and a G-550 electronic intelligence aircraft. They said the operation was coordinated with the United States.

"We are watching very closely," Semmel, who did not confirm U.S. involvement, said. "Obviously, the Israelis were watching very closely."

The State Department confirmed Semmel's remarks, but refused to comment. On Sunday, Defense Secretary Robert Gates said the United States was watching North Korea and Syria "very carefully."

"If such an activity were taking place, it would be a matter of great concern because the president has put down a very strong marker with the North Koreans about further proliferation efforts and obviously any effort by the Syrians to pursue weapons of mass destruction would be a concern," Gates said in a television interview. "I think it would be a real problem."

Former U.S. ambassador to the United Nations, John Bolton, said Syria has long sought nuclear and other WMD capabilities. Bolton said Syria might have agreed to provide uranium enrichment facilities to Iran and North Korea, both of whom have been under international pressure to end their nuclear weapons programs. On Monday, North Korea delayed talks scheduled for Sept. 19 for an end to the nation's nuclear weapons program.

"Syria is very aggressive in pursuing WMD capability," Bolton told the Israeli daily, Jerusalem Post. "It's a diversion game — to carry on even when you are supposed to have halted, as in the case of North Korea. And I'd be surprised if Syria would do anything with North Korea without Iranian acquiescence."