The United States' top diplomat warned Iran on Sunday that time is running out on nuclear negotiations between the Islamic republic and world powers.

"This is not an endless process. ... You can't just talk for the sake of talking," Secretary of State John Kerry told a news conference in Istanbul.

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.

Chinese President Xi Jinping said Sunday that Asia faced "new challenges" to its stability and warned no one should be allowed to throw the region into chaos as tensions mounted over North Korea.

Xi, delivering a speech at an annual international forum on the southern Chinese island of Hainan, did not mention the crisis on the Korean Peninsula or China's territorial disputes with Japan and Southeast Asian nations.

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.

Montenegrins began voting Sunday in a presidential election amid a sluggish economy and high unemployment in the tiny Adriatric EU-candidate country.

Incumbent Filip Vujanovic, a close ally of veteran Montenegrin leader Milo Djukanovic, is tipped to win a third term. He faces former foreign minister Miodrag Lekic, who has managed to get the main opposition groups to back his candidacy.

Venezuela's acting president Nicolas Maduro has accused former U.S. officials Roger Noriega and Otto Reich of plotting to kill him to prevent his victory in next week's presidential elections.

Speaking at a televised campaign event on Saturday, Maduro said the plot also involved "right-wing forces" from El Salvador, which had already dispatched paid assassins to Venezuela to implement the plan.

Some radioactive water may have leaked into the ground from a storage tank at the crippled Fukushima Daiichi nuclear power plant, its operator said Sunday, the latest in a series of troubles at the facility.

The fresh leak comes a day after Tokyo Electric Power Co. (TEPCO) said up to 120 tonnes of contaminated water may have escaped from another of the seven underground reservoir tanks at the tsunami-damaged plant.

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.

Attackers stormed the home of a Nigerian deputy governor on Saturday and slit the throats of two of his guards, while killing nine others in the same village in the restive northeast, police said.

It was unclear who was behind the attack in Midlu village of Adamawa state in the early hours of Saturday, said police spokesman Mohammed Ibrahim. Adamawa Deputy Governor Bala James Ngilari was not at the home at the time.

Nelson Mandela left hospital Saturday after a 10-day stay during which the 94-year-old anti-apartheid icon was treated for pneumonia, the South African president's office said.

"Former president Nelson Mandela has been discharged from hospital today, April 6, following a sustained and gradual improvement in his general condition," presidency spokesman Mac Maharaj said in a statement.