BEIJING/WASHINGTON - China is under mounting pressure from the United States as tensions on the Korean Peninsula continued to run high on Wednesday.

The US will send a delegation headed by Deputy Secretary of State and former special envoy to Pyongyang James B. Steinberg to China on Dec 14 to try to persuade Beijing to put more pressure on Pyongyang.

Other figures in the delegation are National Security Council Senior Director for Asian Affairs Jeffrey Bader, Assistant Secretary of State for East Asia and Pacific Affairs Kurt Campbell, and Special Envoy Sung Kim.

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The visit was announced as the Democratic People's Republic of Korea (DPRK) fired an unknown number of artillery shells that landed on its own side of a disputed maritime border off its west coast on Wednesday morning.

The Republic of Korea (ROK) is also conducting live-fire drills in the area.

The exercises also came as US Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, arrived in Seoul on Wednesday for a two-day trip that will also take him to Japan.

Mullen said there was "no doubt in my mind (that provocations) will continue unless leaders step forward and put Pyongyang in a position where they realize their behavior has to change".

The US and ROK militaries also agreed on Wednesday to stage more joint military drills following last week's giant exercise of the west coast to deter the DPRK.

Mullen's trip to the ROK and Japan follows talks in Washington on Monday between Secretary of State Hillary Clinton and her Japanese and ROK counterparts.

All three voiced grave concerns over the DPRK attacks, and called on China to take actions against them.

On Tuesday, Beijing reiterated that dialogue was the only way to calm escalating tensions on the Korean Peninsula.

But Mullen said the Chinese must do more. "China has (a) unique influence. Therefore, they bear unique responsibility," Mullen told a news conference in Seoul.

Analysts have refuted views that exaggerate China's influence over the DPRK, as China never intervenes into Pyongyang internal affairs.

Jin Canrong, a professor of international studies at Renmin University of China, said the DPRK's firing on Wednesday was a much more restrained response to the toughness showed by the US and ROK with the shells falling into its own waters - not onto ROK territory like on Nov 23.

Jin also said China is unlikely to bend to pressures from the US and its allies, and will continue to insist on peaceful talks.

AP, Reuters and Zhou Wa contributed to this story.