Russia on Thursday warned of a potential "man-made catastrophe" if North Korea restarts an aging plutonium reactor to boost its stockpile of nuclear weapons, after U.S. experts spotted steam rising from the Yongbyon facility.

The reactor, which was completed in 1986, is outdated and North Korea could suffer a major disaster if it is restarted, a Russian diplomatic source told the Interfax news agency.

Less than two weeks before German elections, Chancellor Angela Merkel's conservatives maintained a strong poll lead Wednesday despite an increase for the opposition Social Democrats.

Merkel also boasted a 26-point edge in her personal approval rating over her Social Democratic Party (SPD) rival Peer Steinbrueck ahead of the September 22 vote.

Somalia's al-Qaida-linked Shebab insurgents on Wednesday celebrated the anniversary of the September 11, 2001 attacks with a Twitter eulogy for the "courageous" hijackers.

In a series of posts on Twitter, the Islamists vowed "the mujahideen will continue with their jihad against the West until the world is ruled by one sovereign state, an Islamic state".

More than 550 children have left the ranks of armed groups in the southeastern Democratic Republic of Congo province of Katanga, the United Nations said Wednesday.

"The awareness campaign calling for children to leave armed groups succeeded in demobilizing 557 children between March and August," the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said in a statement.

Georgia on Wednesday voiced "extreme concern" over the presence of Russian troops in its breakaway regions of Abkhazia and South Ossetia.

"I must express our extreme concern over the critical situation in the two regions of Georgia currently under the Russian occupation," Foreign Minister Maia Panjikidze told the U.N. Human Rights Council in Geneva.

Nigerian President Goodluck Jonathan on Wednesday sacked nine ministers in a major cabinet reshuffle amid tensions within the ruling party as his rivals manoeuvre ahead of 2015 elections.

Those sacked included Foreign Minister Olugbenga Ashiru, Education Minister Ruqayyatu Ahmed Rufai and Housing Minister Ama Pepple.

Russian President Vladimir Putin meets Iran's new president for the first time this week, reportedly armed with an offer to supply missile systems and build a second nuclear power reactor that is likely to gladden Tehran and trouble the United States.

President Hasan Rowhani is set to meet Putin on the sidelines of a summit of the Shanghai Cooperation Organization held in Kyrgyzstan on Friday, in the newly-elected centrist cleric's first meeting with a major world leader.

The number of migrants around the world rose above 230 million in 2013 with the United States, Western Europe and the Gulf oil states the biggest draws, the U.N. said Wednesday.

The number who have left their own country has risen from 154 million in 1990 to 232 million and the proportion of migrants in rich countries is growing, said a new U.N. report.

U.S. President Barack Obama on Wednesday mourned the lives lost 12 years ago in the September 11, 2001 attacks, saying "our hearts still ache" for the nearly 3,000 people killed.

Against the backdrop of possible U.S. military action against Syria, Obama marked the 12th anniversary of the 9/11 attacks first at the White House, and then at a solemn Pentagon ceremony attended by families of 9/11 victims and senior officers.

Fighting this week between supporters of the Central African Republic's ex-president and the man who ousted him has killed almost 100 people, officials said Wednesday as an aid group warned of "atrocities" against civilians.

The two days of fighting erupted Sunday in the home region of former president Francois Bozize, who ruled the troubled nation for 10 years until the Seleka rebel coalition overthrew him on March 24 and installed its leader, Michel Djotodia, as president.