Still, Negroponte called Iran's nuclear program a matter of "highest concern." In prepared testimony to the Senate Intelligence Committee, he said that Iran and North Korea are both major threats to US security.

Negroponte raised the possibility that Iran "will acquire a North Korea weapon and the ability to integrate it with the ballistic missile Iran already possesses."

Negroponte spoke as US and European diplomats worked behind the scenes to build support for their decision to report Iran to the UN Security Council over concerns that it seeking nuclear weapons.

The International Atomic Energy Agency's 35-nation board of governors began a two-day meeting on a European draft resolution calling for Tehran to be referred to the Security Council, which can impose sanctions.

Notwithstanding worries about Iran, "Al-Qaida remains our top concern," Negroponte said in his prepared testimony.

"We have eliminated much of the leadership that presided over al-Qaida in 2001," he said, "and US counterterrorism efforts in 2005 continued to disrupt its operations take out its leaders and deplete its cadre."