US President Barack Obama has urged Chinese counterpart Hu Jintao to send "a clear message" to North Korea that its shelling of South Korean territory and other provocations were "unacceptable."

The White House said early Monday the appeal had been made in a telephone call that Obama made to Hu late Sunday to discuss North Korea and other international issues.

"The president emphasized the need for North Korea to halt its provocative behavior and to meet its international obligations, including its commitments in the 2005 Six Party Joint Declaration," the White House said in a statement, following the conversation.

Obama also urged China to work with the United States and other countries "to send a clear message to North Korea that its provocations are unacceptable," the statement added.

The Chinese Foreign Ministry also reported the talks, quoting Hu as saying that "under the current situation, it is imperative that the response is cool and rational and that we firmly prevent a deterioration of the situation."

The telephone call came ahead of high-level talks on Monday between the United States, South Korea and Japan aimed at forging a strategy for dealing with a volatile nuclear-armed North Korea amid allied shows of military force.

The talks hosted by US Secretary of State Hillary Clinton follow North Korea's deadly bombardment of a South Korean border island on November 23, which triggered days of US-South Korean war games in the Yellow Sea.

The consultations come as The Washington Post reported that in an apparent change of its approach to China, the Obama administration has privately started accusing Beijing of "enabling" North Korea to start a uranium enrichment program and to launch attacks on South Korea.

Citing an unnamed senior US official, the newspaper said that Washington is moving to redefine its relationship with South Korea and Japan, potentially creating an anti-China bloc in Northeast Asia.

The report came as South Korea's military began a major live-fire exercise amid high tensions following North Korea's deadly bombardment of a border island last month.

The Joint Chiefs of Staff said the firing exercises by warships or land artillery units had started in 29 locations, including off one of five frontline islands near the disputed Yellow Sea border with the North.

The North on November 23 killed two civilians and two marines and destroyed 29 homes in an artillery attack on Yeonpyeong island, sending regional tensions soaring.

The White House statement said the two presidents had discussed their "common interest in peace and stability in Northeast Asia" and the priority of ensuring the denuclearization of the Korean Peninsula.

"They agreed on the importance of the United States and China working together toward these shared goals," the document pointed out.

Obama also reiterated his condemnation of the North Korean shelling of the South Korean island last month and its pursuit of a uranium enrichment program "in defiance of its obligations."

"The president also highlighted the American commitment to the security of our allies in the region," the statement said.

The United States, South Korea and Japan all refused China's invitation for them and Russia to hold emergency six-party talks in Beijing after the North Korean artillery attack.

The five countries, plus North Korea, make up the long-stalled six-party talks aimed at scrapping Pyongyang's nuclear weapons programs.

Washington, Seoul and Tokyo oppose a return to the negotiations until Pyongyang shows it is serious about disarmament.

In November, a US scientist revealed he had been shown a new uranium enrichment plant equipped with at least 1,000 centrifuges at the North Korea's Yongbyon nuclear complex outside the capital Pyongyang.

The display sparked fears that North Korea, which has already carried out explosive tests of two plutonium nuclear devices, will have another avenue to build atomic bombs.

According to the White House, Obama also raised in the conversation the issue of Iran.

"He stressed the importance of P5+1 unity in order to address Iran's nuclear program," the statement said.

The P5+1 formula refers to five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- plus Germany.

The group began talks with Iran on the deepening standoff over its nuclear program in Geneva Monday.