Warning the Democratic People's Republic of Korea from its door step, US President Barack Obama said Pyongyang risks deepening its isolation if it proceeds with a planned long-range rocket launch.

"(The DPRK) will achieve nothing by threats or provocations," Obama said during a news conference on Sunday in Seoul, where he was to attend a nuclear security summit.

Obama spoke fresh off his first visit to the tense Demilitarized Zone, the heavily patrolled no-man's land between the DPRK and the Republic of Korea, where he peered long and hard at the DPRK.

From the DMZ, Obama returned to Seoul for a private meeting with ROK President Lee Myung-bak. Both leaders warned there would be consequences if the DPRK proceeds with its plans to launch a satellite using a long-range rocket next month, a move the US and other powers say would violate a UN ban on nuclear and missile activity because the same technology could be used for long-range missiles.

Obama said the launch would jeopardize a deal for the US to resume stalled food aid to the DRPK and may result in the tightening of harsh economic sanctions on the country.

The DPRK walked away from the Six-Party Talks in 2009, which group the US, China, Russia, Japan, the ROK and the DPRK. Years of negotiations had succeeded in ending part of the DPRK's nuclear program but failed in stopping it from building and testing nuclear devices and long-range missiles.

Also on Sunday, Obama urged China to use its influence to stop the DPRK's "bad behavior" in Pyongyang's nuclear standoff with the West and hinted at tougher sanctions if the state goes ahead with the missile launch.

"I believe that China is very sincere that it does not want to see (the DPRK) with a nuclear weapon," he said. "But it is going to have to act on that interest in a sustained way."

"My suggestion to China is that how they communicate their concerns to (the DPRK) should probably reflect the fact that the approach they have taken over the last several decades has not led to a fundamental shift in (the DPRK's) behavior," Obama said.

"The continuity of Pyongyang's behavior is precisely because Washington and Seoul haven't changed their attitude toward it," said Chen Qi, an expert on East Asian studies at Tsinghua University.

"Obama's words may add more uncertainty to Sino-US ties and have a negative influence on the ties between the two countries," said Chen, urging Washington to rethink its own policies on Pyongyang's nuclear issues.

Obama's visit to the DMZ took place as people in the DPRK marked the end of the 100-day mourning period for its former leader Kim Jong-il, who died of a heart attack in December.

Warning the Democratic People's Republic of Korea from its door step, US President Barack Obama said Pyongyang risks deepening its isolation if it proceeds with a planned long-range rocket launch.

"(The DPRK) will achieve nothing by threats or provocations," Obama said during a news conference on Sunday in Seoul, where he was to attend a nuclear security summit.

Obama spoke fresh off his first visit to the tense Demilitarized Zone, the heavily patrolled no-man's land between the DPRK and the Republic of Korea, where he peered long and hard at the DPRK.

From the DMZ, Obama returned to Seoul for a private meeting with ROK President Lee Myung-bak. Both leaders warned there would be consequences if the DPRK proceeds with its plans to launch a satellite using a long-range rocket next month, a move the US and other powers say would violate a UN ban on nuclear and missile activity because the same technology could be used for long-range missiles.

Obama said the launch would jeopardize a deal for the US to resume stalled food aid to the DRPK and may result in the tightening of harsh economic sanctions on the country.

The DPRK walked away from the Six-Party Talks in 2009, which group the US, China, Russia, Japan, the ROK and the DPRK. Years of negotiations had succeeded in ending part of the DPRK's nuclear program but failed in stopping it from building and testing nuclear devices and long-range missiles.

Also on Sunday, Obama urged China to use its influence to stop the DPRK's "bad behavior" in Pyongyang's nuclear standoff with the West and hinted at tougher sanctions if the state goes ahead with the missile launch.

"I believe that China is very sincere that it does not want to see (the DPRK) with a nuclear weapon," he said. "But it is going to have to act on that interest in a sustained way."

"My suggestion to China is that how they communicate their concerns to (the DPRK) should probably reflect the fact that the approach they have taken over the last several decades has not led to a fundamental shift in (the DPRK's) behavior," Obama said.

"The continuity of Pyongyang's behavior is precisely because Washington and Seoul haven't changed their attitude toward it," said Chen Qi, an expert on East Asian studies at Tsinghua University.

"Obama's words may add more uncertainty to Sino-US ties and have a negative influence on the ties between the two countries," said Chen, urging Washington to rethink its own policies on Pyongyang's nuclear issues.

Obama's visit to the DMZ took place as people in the DPRK marked the end of the 100-day mourning period for its former leader Kim Jong-il, who died of a heart attack in December.