Updated

A top U.S. official on Tuesday questioned North Korea's (search) commitment to six-nation nuclear disarmament talks but said Washington would never abandon the process.

The talks, involving the two Koreas, the United States, China (search), Japan and Russia, are aimed at ending Pyongyang's nuclear ambitions. They have been stalled since June, and the North has refused to return to the negotiating table because of what it calls a hostile U.S. policy toward Pyongyang.

It has also sought an apology over Secretary of State Condoleezza Rice's (search) labeling of the country as one of the world's "outposts of tyranny."

Christopher Hill, the chief U.S. negotiator in the multinational talks, told reporters in Manila that conditions imposed by the North for the resumption of negotiations had stalled a "very serious process."

"For the North Koreans to be fixating on one statement and not addressing, or not even being willing to address, the fundamental issues that bring us together, really calls into question how serious they are about the process," he said. "For them to really be talking about seeking apologies ... is really not a serious answer to a serious issue."

Hill urged the international community, particularly China, to continue pressing North Korea to return to the six-way talks. Beijing has already hosted three unsuccessful rounds of talks. A fourth round planned for last September was postponed when the North refused to attend.

"One option that is not available to us is to walk away from this problem," he said.

During a visit to Beijing last week, Rice said Washington would "have to look at other options" if the North doesn't return to the nuclear talks. She didn't elaborate, but they would likely include seeking sanctions through the U.N. Security Council.

Rice has repeatedly said the United States has no plans to attack the North.

In February, North Korea claimed it's built nuclear weapons for self-defense and would indefinitely boycott the international talks. This month it claimed it had bolstered its arsenal. The claims have not been verified.