US President George W Bush chided China and North Korea Wednesday on their human rights records but defended his decision to attend this week's Beijing Olympics opening ceremony.

The US leader, in a strong message to North Korean leader Kim Jong-Il, said Kim would continue to lead "the most sanctioned regime in the world" unless he honours nuclear disarmament commitments.

Bush said it was premature to drop the communist North from the "axis of evil" he had proclaimed back in 2002.

He was speaking at a press conference after summit talks with South Korean President Lee Myung-Bak.

Bush has been accused of overlooking China's rights record with his decision to attend Friday's opening of the Games.

But he said he did not need the Olympic issue to express his views on religious and other freedoms.

"I have been meeting Chinese leaders for 7 1/2 years and my message has been the same: you should not fear religious people in your society. As a matter of fact, religious people will make your society a better place," Bush said.

Bush said China's leaders "ought to welcome people being able to express their minds, and to the extent that people aren't able to do that and people aren't able to worship freely, (it) is a mistake."

The Games, he said, is an athletic event. "But it's also an opportunity to say to the Chinese people, we respect your traditions, we respect your history," he added.

Bush and Lee reaffirmed a commitment to strengthen their countries' alliance forged after the 1950-53 Korean War.

The US leader was to address troops at the Yongsan army base - party of a 28,500-strong American military contingent in the country - before departing for Thailand later on Wednesday.

Bush, under fire from domestic critics who say he has conceded too much to Pyongyang, reserved his strongest words for North Korea.

"I'm concerned about North Korea's human rights record, I'm concerned about its uranium enrichment activities as well as its nuclear testing and proliferation and its ballistic missile programmes. The best way to approach and answer the concerns is strong verification measures. That's where we are in the six-party talks," he said.

South Korea and the United States, along with China, Japan and Russia, have since 2003 been negotiating a denuclearisation deal with North Korea, which tested an atomic weapon in October 2006.

The North handed over details of its bomb-making plutonium nuclear programme in June as part of a six-nation pact, and Bush announced his intention to remove it from a terrorism blacklist.

But Washington says it must first agree ways to verify the declaration.

Bush said August 12 is the earliest the North can be taken off the blacklist, which blocks access to US economic assistance and to aid from multilateral bodies.

Before that can happen, he said, "They have got to show a verification regime that we can trust."

The United States accuses the North of operating a secret highly enriched uranium weapons programme, a charge it denies.

The North also rejects US claims that it helped Syria build an apparent atomic reactor destroyed in an Israeli air raid last September.

Bush welcomed the North's moves to disable its Yongbyon atomic complex but said it has much more to do under the six-party deal.

He said Kim Jong-Il had a choice to make: "You can verifiably do what you say you're going to do, or you continue to be the most sanctioned regime in the world."

South Korea deployed some 23,000 police for Bush's visit, which followed months of protests against the import of US beef.

Police used water cannon and arrested 167 people to break up protests Tuesday evening and overnight against the beef pact and Bush's visit.

Protesters claim US beef carries the risk of mad cow disease but rallies have largely subsided since a new safeguards pact.

Police said 2,700 people took part in a rally Tuesday evening, a fraction of the number earlier this summer. Vastly more people rallied earlier on Tuesday to show support for Bush's visit.