Updated

South Korea's president vowed Thursday to boost security around islands near the site of a North Korean artillery attack while the North warned of more retaliation if the South carries out any "reckless military provocations."

Seoul and Washington also increased pressure on China to use its influence on ally North Korea to ease soaring tensions that erupted after an exchange of fire Tuesday that left four South Koreans dead — including two civilians. China urged both sides to show restraint.

The North's bombardment of a tiny South Korean island along a disputed maritime frontier has alarmed world leaders including President Barack Obama, who reaffirmed plans for joint maneuvers with Seoul in the Yellow Sea starting Sunday.

"We should not let our guard down in preparation for another possible North Korean provocation," South Korean President Lee Myung-bak said during an emergency meeting on security and economic repercussions from the attack, according to Yonhap news agency.

The U.S.-South Korean drills involving aircraft carrier USS George Washington, although previously scheduled, are sure to infuriate North Korea. The North made no specific mention of those exercises in its statement but warned that its military would "launch second and third strong physical retaliations without hesitation if South Korean warmongers carry out reckless military provocations."

The North's statement said Washington was to blame for South Korean artillery exercises earlier in the week near disputed waters which prompted the North to respond with its artillery barrage on Yeongpyeong island Tuesday.

Washington "should thoroughly control South Korea," it said. The warning was issued by North Korea's military's mission at the truce village of Panmunjom and was carried by the country's official Korean Central News Agency.

The Obama administration urged China to rein in its ally North Korea, with the chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, saying, "We really think it's important for the international community to lead, but in particular China."

Chinese Premier Wen Jiabao called on all sides to show "maximum restraint" over recent tensions on the Korean Peninsula and says his country opposes military provocations of all forms.

Wen also urged the international community to work to ease tensions. He repeated Chinese calls for renewed six-nation talks aimed at persuading North Korea to dismantle its nuclear programs.

Wen said those talks, involving the two Koreas, China, Russia, Japan and the United States, are the best way to ensure stability on the peninsula and its denuclearization.

Wen's remarks were made in Russia on Wednesday on a state visit and posted on the Chinese Foreign Ministry's website.

South Korea said it will increase diplomatic efforts toward China to secure Beijing's help over North Korea's provocation, according to Yonhap. Repeated calls to the presidential office seeking confirmation went unanswered.

Residents of Yeongpyeong who evacuated the island and began arriving at the South Korean port of Incheon on Wednesday told harrowing tales of fiery destruction and narrow escapes.

Ann Ahe-ja, one of hundreds of exhausted evacuees from Yeonpyeong island arriving in the port of Incheon on a rescue ship, said the artillery barrage that killed four people — two of them civilians — had caught her by surprise.

"Over my head, a pine tree was broken and burning," Ann told AP Television News on Wednesday. "So I thought 'Oh, this is not another exercise. It is a war.' I decided to run. And I did."

About 10 homes suffered direct hits and 30 were destroyed in the midafternoon barrage, according to a local official who spoke by telephone from the island just seven miles (11 kilometers) from the North Korean shore. About 1,700 civilians live on Yeonpyeong alongside South Korean troops stationed there.

"I heard the sound of artillery, and I felt that something was flying over my head," said Lim Jung-eun, 36, who fled the island with three children, including a 9-month-old strapped to her back. "Then the mountain caught on fire."

Many of those evacuated from Yeonpyeong had spent the night in underground shelters and embraced tearful family members on arrival in Incheon.

The shower of artillery from North Korea was the first to strike a civilian population. In addition to the two marines killed, the bodies of two men, believed in their 60s, were pulled from a destroyed construction site, the coast guard said. At least 18 people — most of them troops — were injured.

Officials in Seoul said there could be considerable North Korean casualties. North Korea's main Rodong Sinmun newspaper published a military statement accusing South Korea of triggering the exchange, but did not mention any casualties.