US President George W Bush and South Korean President Lee Myung Bak called Wednesday on North Korea to meet its denuclearization pledge.

Pyongyang has "a lot to do" before the United States fulfils one of its top demands in nuclear talks, to be taken off the US list of state sponsors of terrorism, Bush said at a news conference with Lee. One of those tasks is establishing a process to verify that it is fulfilling its nuclear commitments, the US president said.

The United States said it would remove communist North Korea from the terrorism list as early as Monday if a rigorous verification process is established; however, discussions have stalled.

"I don't know whether or not they're going to give up their weapons," Bush said.

The US president said he was concerned about North Korea's uranium-enrichment activities, its nuclear testing and proliferation, and its ballistic missile programmes.

"The best way to approach and answer those concerns is for there to be strong verification measures," added Bush, who had named North Korea as part of an "axis of evil" in 2002 for its weapons proliferation before agreeing to negotiate with it.

In Bush's third meeting with Lee, the two conservative presidents said the United States and South Korea would integrate the communist state with the international community if, among other conditions, Pyongyang allows international inspections to verify its nuclear disarmament.

North Korea has been offered economic and humanitarian aid if it dismantles its nuclear programme in its negotiations with the United States, China, Russia, South Korea and Japan, which have been going on since 2003.

Lee and Bush also said a free trade agreement their two countries signed would boost trade, increase economic growth and create jobs in both the United States and South Korea. They urged their legislatures to approve the pact this year.

Bush, who leaves office in January, arrived in South Korea Tuesday on the first stop of a weeklong, three-nation Asia trip.

After meeting with US soldiers, he is to leave South Korea for Thailand Wednesday. He then is to go to Beijing, where his stay includes taking part in Friday's opening ceremony of the Summer Olympic Games.