Seoul, South Korea (CNN) -- South Korea and the United States started joint military exercises Sunday, U.S. Forces Korea spokesman David Oten told CNN, prompting a furious response from North Korea.

The naval operations are "no more than an attempt to find a pretext for aggression and ignite a war at any cost," North Korea's official Korean Central News Agency said, warning that the drills "are putting the Korean Peninsula at a state of ultra-emergency."

North Korea warned of unpredictable "consequences" if the United States sends an aircraft carrier to the Yellow Sea for the military maneuvers.

The divided peninsula, tense at the best of times, has been near the boiling point since Tuesday, when North Korea shelled a South Korean island, killing four people.

China called Sunday for an emergency meeting of the six major powers involved in talks about the Korean peninsula.

Top diplomats from the six nations need to meet soon to "maintain peace and stability on the peninsula and ease the tension" in the region, Beijing's special representative for the region, Wu Dawei, said Sunday.

South Korea said Sunday it did not think the time was right for a resumption of the Six-Party talks, then added that its comment was not a response to China's call for an emergency meeting, which Seoul said it would "bear in mind."

But Seoul was extremely cautious about the proposal, given what it called the North's "military provocation," and recent nuclear moves.

U.S. Sen. John McCain, R-Arizona, said on CNN's "State of the Union" Sunday that the flare-up exposed the failure of "continued appeasment" of North Korea by Republican and Democratic administrations. He said the United States has given North Korea more than $1 billion in aid over the past 15 years with the goal of getting them to the negotiating table.

"It seems the purpose of everything is to get the North Koreans to the table," McCain said. "The North Koreans' only claim to their position on the world stage is their nuclear capability. And they have a terrible, most repressive, oppressive regime in the world. They have hundreds of thousands of people in slave labor camps. And all of that seems to be sacrificed in the altar of, quote, 'negotiations.'"

Significant pressure should have been placed on North Korea long ago, said McCain, the ranking Republican on the Senate Armed Services Committee.

A top Chinese envoy met South Korea's President Lee Myung-bak Sunday and a high-ranking North Korean official will visit Beijing this week, China's Xinhua news agency said.

North Korea said the South provoked the attack on Yeonpyeong Island because shells from a South Korean millitary drill landed in the North's waters.

A group of 124 people left Yeonpyeong Island by boat Sunday.

The South Korean defense ministry is urging journalists to leave the island voluntarily because of the instability, the Foreign Correspondents' Club of Seoul said Sunday. The ministry expects most journalists to leave Sunday night.

South Korea said Sunday another shell had accidentally been fired during a land-based military exercise, separate from the naval drills with the Americans.

The shell, fired by a unit based near Munsan, South Korea, landed on the South Korean side, a defense ministry spokesman told CNN. South Korea notified the North of the "accidental firing," and there has been no response, the spokesman said.

Earlier Sunday, the United States and South Korea began assembling ships for the exercises off the west coast of the Korean peninsula in the Yellow Sea, a source at the South Korean Joint Chiefs told CNN.

KCNA warned Sunday what could happen if the country perceives its waters are infringed upon.

"The DPRK [Democratic People's Republic of Korea] will deal a merciless military counter-attack at any provocative act of intruding into its territorial waters in the future," the state news agency said.

It called reports of civilian casualties part of South Korea's "propaganda campaign" and accused the "enemy" of creating "a human shield by deploying civilians around artillery positions and inside military facilities before the launch of the provocation."

"If the U.S. brings its carrier to the West Sea of Korea at last, no one can predict the ensuing consequences," said KCNA, referring to the aircraft carrier USS George Washington, which is set to join South Korea's forces near the coasts of China and North Korea for the four-day military drill.

U.S. State Department spokeswoman Nicole Thompson called the claims "outrageous."

"This is just another example of North Korea's own internal propaganda. The North Koreans for many years, including the Cheonan warship incident, have taken provocative action. This didn't have anything to do with U.S. actions," Thompson told CNN, referring to the sinking of a South Korean ship in March that left 46 people on board dead.

The United States and South Korea blame the sinking on the North, which has consistently denied responsibility.

Diplomats, seeking a lessening of tensions and a return to the six-party talks with North Korea over the country's nuclear aspirations, have busily labored to avert more hostilities. The United States, China, Japan, Russia, South Korea and North Korea are the six countries that have been involved in the talks, which were put on hold in 2008.

The violence has sparked anger and political turmoil in South Korea. The country's defense minister, Kim Tae-young resigned after the exchange of fire, and veterans of the South Korean military protested Saturday on the streets of Seoul, stating they were angry that their country's government had not done enough to respond to the North's shelling.

The tense maritime border between the two Koreas has become the major military flashpoint on the Korean peninsula in recent years.

The Yeonpyeong attack was the first direct artillery assault on South Korea since 1953, when an armistice ended fighting. North and South Korea are still technically at war.

Journalists Andrew Salmon and Jiyeon Lee and CNN's Stan Grant and Tim Schwarz contributed to this report.