Despite North Korean leader Kim Jong-il’s pledge this week to unconditionally return to the long-stalled nuclear disarmament talks, the communist state still has far to go before the deadlock is fully resolved, officials in Seoul and Washington said Thursday.

On the last day of his week-long visit to Russia Wednesday, Kim held summit talks with President Dmitry Medvedev, promising to work on introducing a moratorium on testing and spent nuclear fuel processing, and allow construction of a key gas pipeline.

Pyongyang has been hoping to persuade dialogue partners to restart the six-nation nuclear disarmament talks, through which it had received food and fuel aid for many years until the negotiations halted at the end of 2008. It conducted its second nuclear test shortly afterwards.

The negotiations involve the two Koreas, the U.S., Russia, China and Japan.

Through its official news agency, Pyongyang said its leader shared “the view that the six-party talks should be resumed without any preconditions at an early date” during his talks with the Russian president, failing to mention Kim’s reported promise to impose a moratorium on nuclear testing.

While the Russian leader called the meeting as “open and substantive,” South Korea downplayed Kim’s promise as “nothing new” and “somewhat ceremonial.”

“We haven’t been able to decide on the exact intentions of North Korea based merely on what was announced by the Russian presidential office,”

Shin Maeng-ho, vice spokesman of South Korean Foreign Ministry, told a regular press briefing Thursday. “We are waiting for Russia to brief us on the details of the talks.”

Another senior official here said Kim “was merely repeating the position North Korea has had for the past several months.

“To return to the negotiation table, North Korea has to do more than that. It needs to prove its commitment to disarm with action not words,” he said on the condition of anonymity.

Washington also called the reported offer “welcome but ... insufficient.”

“If it’s true, (it’s a) welcome first step, but far from enough ... to resume the six-party talks,” State Department spokeswoman Victoria Nuland told reporters in Washington.

Noting North Korea’s disclosure of new uranium enrichment facilities, largely seen as a second path to developing nuclear weapons, Nuland called the issue a matter of serious concern. The North conducted two plutonium-based weapons tests each in 2006 and 2009.

“As you know, their disclosure last November of uranium enrichment facilities remains a matter of serious concern to us, and these activities are a clear violation of their obligations under U.N. Security Council Resolutions,” she said.

South Korea, still trying to overcome hard feelings toward its northern rival for last year’s deadly attacks, also expressed skepticism about the gas pipeline project Moscow has been pursuing.

During his talks with Medvedev, Kim expressed support for the trilateral natural gas pipeline deal with Russia and South Korea, according to the Russian leader.

Moscow has long been asking to build a pipeline to stream Russian natural gas through the North’s territory to the South.

Once the rare deal is finalized, Pyongyang, which has relied heavily on outside aid to feed its population of 24 million since the late 1990s, could earn up to $100 million each year, according to Seoul’s estimation.

“For this process to move forward in earnest, the two Koreas must have faith in one another,” an official at Seoul’s Unification Ministry, which handles affairs with Pyongyang, told reporters on the condition of anonymity.

“Although we fully recognize the need for this gas pipeline and the meaning of it, we first want to see North Korea prove itself as a responsible partner in relations with us as well as the rest of the international community,” the official said.

The communist North apparently torpedoed a South Korean warship and bombarded a border island in March and November last year, respectively, killing up to 50 South Koreans including two civilians.

Meanwhile, the North Korean leader is believed to have headed to China on his way back home from Russia as Seoul’s chief nuclear envoy also headed to Beijing for talks over how to revive the denuclearization talks.

Quoting eyewitnesses, reports said Kim’s train was seen in the Russia-China border city of Manzhouli where security had been reinforced near the station. Kim may meet with Chinese officials to discuss the results of his talks with the Russian leader, they said.

Seoul’s chief nuclear envoy Wi Sung-lac also arrived in Beijing Thursday to discuss pending issues with his Chinese counterpart Wu Dawei.

Before departing to China, Wi said he plans to “assess the North Korean nuclear issue and situation on the Korean Peninsula and discuss a wide range of views on how to move the process of discussions forward,” with Wu.

By Shin Hae-in (hayney@heraldcorp.com)