WASHINGTON - US officials denied that a rare series of meetings between senior US and North Korean diplomats marked a break with the Bush administration's long-standing refusal to negotiate directly with the Stalinist regime.

"This is not an instance of bilateral negotiations," Tony Snow, President George W. Bush's spokesman, said of the three days of talks on North Korea's nuclear program this week between chief US negotiator Christopher Hill and his North Korean counterpart, Kim Kye-gwan.

Hill and Kim met in Berlin for several hours between Wednesday and Thursday in their first one-on-one sessions held outside of a multi-party format in Beijing since Bush came to office in 2001.

Hill, the assistant secretary of state for East Asia and the Pacific, described the talks aimed at getting North Korea to give up its nuclear weapons as "substantive" and "useful".

The meetings fueled speculation that Bush, mired in the Iraq crisis and in dire need of a foreign policy success, had loosened the reins on his diplomats so they could deal more directly with formerly taboo regimes.

But Snow and other officials insisted the Berlin contacts broke no new ground and were part of an ongoing set of six-party negotiations launched in 2003 and resurrected in December after a year-long boycott by the North Koreans.

Hill met with Kim in hopes of organizing another round of the broader talks later this month or early next month in the Chinese capital, State Department deputy spokesman Tom Casey said.

Their talks "certainly don't represent anything particularly new or different from what we've done before," Casey said.

The six-party talks -- involving China, Japan, the two Koreas, Russia and the United States -- are aimed at convincing North Korea to abandon its nuclear weapons program in exchange for security guarantees, economic aid and a normalization of relations with Washington.

North Korea returned to the talks after being hit with international sanctions in October for having carried out its first nuclear test explosion.

Five days of negotiations ended in deadlock, with the North Koreans refusing to broach the subject of nuclear weapons unless Washington backed off financial sanctions imposed a year earlier on a Macau bank accused of money-laundering for Pyongyang.

The US has agreed to discuss the sanctions in parallel with the nuclear disarmament talks.

North Korea has long sought direct bilateral dealings with the United States as a way to boost its status internationally and avoid linkages with other issues involving Washington's regional allies.

Bush and Secretary of State Condoleezza Rice have refused, pointing to failed denuclearization negotiations carried out with Pyongyang by the previous administration of President Bill Clinton as proof that two-way talks with the erratic North Koreans cannot work.

They argue that the combined pressure of the multi-party format, notably including North Korea's primary benefactor, China, is needed to ensure Pyongyang honors any future agreements.

Bush and Rice similarly have refused calls to engage directly with Iran and Syria as part of the administration's latest push to stabilize Iraq and resolve crises in Lebanon and between Israel and the Palestinians.

Their stance has been widely criticized by the opposition Democrats who gained control of Congress in November as well as by leaders of Bush's won Republican party and former officials from both political camps.

The State Department's Casey on Thursday reaffirmed the administration's refusal to deal with Iran unless it complies with UN resolutions demanding it halt uranium enrichment activities many believe are part of a program to develop nuclear weapons.

Rice told Congress last week that she would meet "any time, anywhere" with the Iranians once they meet the UN demands.

"It's pretty clear that if the Iranians want to have a dialogue with the United States, there's an avenue open to them and we'd very much like them to take us up on it," Casey said.