The U.N. atomic watchdog chief on Monday called North Korea's drive to restart a nuclear site "troubling" and said his team could not detect whether the regime planned a new nuclear test due to a lack of access.

Yukiya Amano, director general of the International Atomic Energy Agency, said the watchdog had observed Pyongyang's efforts to rebuild parts of its Yongbyon nuclear site amid a showdown with South Korea and the United States.

North Korea's decision to pull its workers out of the Kaesong joint industrial zone and suspend all commercial operations at the complex "cannot be justified," South Korea said Monday.

"North Korea's unilateral decision to push ahead with this measure cannot be justified in any way and North Korea will be held responsible for all the consequences," the Unification Ministry's spokesman said in a statement.

Russian President Vladimir Putin on Monday welcomed a US decision to delay the test of an international ballistic missile to avoid stoking tensions with North Korea.

"I think the United States took a very important step in delaying the test of a ballistic missile," he told reporters at an industrial fair in Germany, speaking through an interpreter.

U.N. chief Ban Ki-moon made an urgent appeal to North Korea on Monday to refrain from "any further provocation", following reports that the increasingly isolated state is preparing a fresh missile test launch.

"The Democratic People's Republic of Korea cannot go on like this, confronting and challenging the authority of the (U.N.) Security Council and the international community," Ban said in The Hague.

Japan has ordered its armed forces to shoot down any North Korean missile headed towards its territory, a defense ministry spokesman said Monday as speculation grows Pyongyang may fire one this week.

Defense Minister Itsunori Onodera issued the order, which will see Aegis destroyers equipped with sea-based interceptor missiles deployed in the Sea of Japan, the defense official said.

China said it had asked North Korea to ensure the safety of its diplomats after a warning that missions should consider evacuating, and that it would not tolerate "troublemaking" on its doorstep.

North Korean authorities on Friday told embassies in Pyongyang that their safety could not be guaranteed if a conflict breaks out, after weeks of escalating threats against the United States and South Korea.

Japan will order its armed forces to shoot down any North Korean missile headed towards its territory, press reports said Sunday as Pyongyang was reportedly readying to fire one.

The order may be issued by Defense Minister Itsunori Onodera on Sunday or "in a day or two," the Yomiuri newspaper and the Jiji news agency reported.

The U.S. has delayed a ballistic missile test to avoid stoking tensions with North Korea, which has warned diplomats to consider evacuating from Pyongyang as a nuclear crisis brews on the Korean peninsula.

The Pentagon's disclosure that it would reschedule the intercontinental missile test due in California next week comes as the international community grows increasingly nervous that the situation could spiral out of control.

"The security of the German embassy and its exposure to danger are continually being evaluated," the German foreign ministry said in a statement. "For now, the embassy can continue working."

"Regarding the embassy's security, there are ongoing consultations, particularly with the other foreign partners who also have embassies" in the country, the statement said.

The United States is pressuring China's new President Xi Jinping to crack down on the regime in North Korea or face an increased U.S. military presence in the region, The New York Times reported late Friday.

Citing unnamed administration officials, the newspaper said the recent U.S. exchanges with China included a phone call from President Barack Obama to Xi.