SEOUL, South Korea - North Korea insisted today it won't dismantle its nuclear weapons program until the U.S. gives it civilian nuclear reactors, casting doubt on a disarmament agreement reached a day earlier during international talks.

Washington reiterated its rejection of the reactor demand and joined China in urging North Korea to stick to the agreement announced Monday in which it pledged to abandon all its nuclear programs in exchange for economic aid and security assurances.

North Korea's new demands underlined its unpredictable nature and deflated some optimism from the Beijing agreement, the first since negotiations began in August 2003 among the two Koreas, the United States, China, Japan and Russia.

"The U.S. should not even dream of the issue of (North Korea's) dismantlement of its nuclear deterrent before providing (light-water reactors), a physical guarantee for confidence-building," the North's Foreign Ministry said in a statement carried by the official Korean Central News Agency.

U.S. officials dismissed the demand.

"This is not the agreement that they signed, and we'll give them some time to reflect on the agreement they signed," State Department spokesman Sean McCormack said in New York on Monday.

CAIRO, Egypt - Al-Qaida deputy leader Ayman al-Zawahri said in a statement broadcast Monday that his terror network carried out the July 7 London bombings, marking the group's first direct claim of responsibility for the attacks that killed 52 people.The Egyptian-born militant also criticized the legitimacy of Sunday's parliamentary elections in Afghanistan and condemned Pakistan - the one-time ally of Afghanistan's deposed Taliban regime - for forging strong ties with the United States."The blessed London attack was one which al-Qaida was honored to launch against the British Crusader's arrogance and against the American Crusader aggression on the Islamic nation for 100 years," al-Zawahri said in the tape aired on Qatar-based al-Jazeera TV."In their final testament, the heroic brothers in the London attacks ... provided great lessons to the Islamic nation and Muslims in Pakistan to oppose the infidels," said al-Zawahri, who wore a black turban and white shirt and spoke to someone off-camera who was interviewing him. The attacks also killed the four bombers."This blessed attack revealed the real hypocritical face of the West," said al-Zawahri in his latest tape.By The Associated Press