The Republic of Korea and the United States launched a joint military exercise on Monday as Pyongyang cut off its hotline with Seoul to denounce the drill.

Also on Monday, the ROK's new foreign minister, Yun Byung-se, said that the security situation on the Korean Peninsula has become "very grave", Yonhap News Agency reported.

Meanwhile, China again urged all parties to act with restraint and resolve the issue through political dialogue. Observers said the possibility of confrontation between the ROK and the Democratic People's Republic of Korea is not high, but no one should increase uncertainty on the peninsula.

"The current situation on the peninsula is highly complex and sensitive," said Chinese Foreign Ministry spokeswoman Hua Chunying at a daily news briefing.

"China calls on relevant parties to exercise calm and restraint, and avoid actions that might further escalate tensions."

Beijing urges all relevant parties to find effective ways for a complete resolution of the issue within the framework of the Six-Party Talks, Hua said, adding that China would like to work with all parties.

Hua's remarks came as a two-week "Key Resolve" military exercise jointly conducted by the ROK and the US began on Monday, while the DPRK's state media said that the 1953 armistice agreement that halted the Korean War is no longer valid.

Controversial drill

Pyongyang had earlier condemned the joint maneuvers as a provocative invasion rehearsal. "Key Resolve" is largely a computer-simulated exercise, but still involves the mobilization of more than 10,000 ROK forces and 3,500 US military personnel. About 28,500 US troops are stationed in the ROK.

This year is the first time the ROK's Joint Chiefs of Staff has planned and executed such a combined exercise, said US General James Thurman, head of the Combined Forces Command.

The ROK is scheduled to assume wartime operational control of the combined forces in December 2015.

Although it is a routine military drill, it will add to the tension on the peninsula, said Wang Fan, assistant president of China Foreign Affairs University. The US and the ROK attempted to deter the DPRK with such exercises, but the drill will further provoke Pyongyang rather than intimidate it, he added.

The ROK plays a bigger role in this routine military drill this year, which has angered the DPRK, said Zhang Liangui, an expert on Korean Peninsula studies at the Party School of the Communist Party of China Central Committee.

The DPRK will upgrade its security level, and the possibility of military accidents cannot be ruled out, Zhang said.

Hotline cut

With regard to the hotline, the ROK's Unification Ministry confirmed that the DPRK did not answer calls from the ROK on Monday, according to AFP.

The two sides habitually speak twice a day on the hotline, installed in 1971. The DPRK has severed it five occasions in the past, the most recent being in 2010.

ROK President Park Geun-hye said in her first state conference that Seoul should firmly deal with Pyongyang's provocation, but should not give up pushing the trust-building process on the Korean Peninsula, Yonhap said.

Contact the writers at zhouwa@chinadaily.com.cn and zhangyunbi@chinadaily.com.cn.