South Korea deployed some 13,000 police and soldiers to guard President Barack Obama during his visit but pro-US demonstrators heavily outnumbered protesters in central Seoul Thursday.

"Welcome Obama!" chanted an estimated 3,000 activists lining the streets near the US embassy as his motorcade passed by en route to talks with President Lee Myung-Bak.

Demonstrators held placards reading "We support strong US-Korea alliance" and "We love Obama".

The rally was led by veterans wearing military uniforms who denounced North Korea's nuclear weapons programme, an issue likely to dominate the summit talks.

Dozens of police buses surrounded the embassy and thousands of riot police were posted in central Seoul and around the Grand Hyatt hotel in Namsan district where the president stayed.

Dozens of activists protesting at South Korea's decision to send troops to Afghanistan had rallied outside the embassy Wednesday before Obama arrived on the last leg of his Asian tour.

Local rights advocates urged Obama Wednesday to speak out more strongly against North Korea's human rights abuses.

New York-based Human Rights Watch has also called on him and Lee to take a strong stance on the issue.

It said in a statement Wednesday the leaders "should make a public commitment to address human rights concerns in North Korea as well as the plight of North Korean refugees (in China)."