An unusually large blanket of thick fog descended on European airports Monday, causing scores of flight cancellations from London Heathrow, the continent's busiest, and delays at key hubs including Amsterdam and Frankfurt.

Eurocontrol, the European air traffic control organization, said the opaque vapour also caused delays in Paris, Stuttgart, Hamburg, Berlin, Luxembourg and Brussels, though Britain was the worst affected.

Four South African police officers were arrested Monday on murder charges after a video emerged of an execution-style killing of a suspected robber on a suburban street.

Footage from closed circuit television showed police firing at the man from close range as he lay on the ground in Krugersdorp, a town west of Johannesburg.

He once wanted to "wipe out" Twitter and compared social media to a "murderer's knife," but President Recep Tayyip Erdogan couldn't resist sending a tweet on Monday to celebrate his party's election victory. 

The famously tech-phobic Erdogan issued a series of tweets on his official account after the Justice and Development Party (AKP) he co-founded reclaimed its parliamentary majority in Sunday's vote.

Two French pilots who slipped out of the Dominican Republic in mysterious circumstances after being convicted of cocaine trafficking were formally arrested and remanded in custody in France on Monday.

Pascal Fauret, 55, and co-pilot Bruno Odos, 56, were arrested early Monday at their homes near the southeast city of Lyon.

Russian police searched the offices of a Tatar TV channel in Crimea early Monday as well as homes of its employees, its deputy director told AFP, the latest raid against the once popular network which was forced to go off air in April.

"About 20 armed men from the FSB (security service) came to my house at 5:30 am and seized all documents, computers and telephones," said Lilia Budzhurova, the deputy director of ATR channel, adding that her lawyer was not allowed to be present.

The Vatican has arrested a Spanish prelate and social media expert for allegedly stealing and leaking classified documents in the second such scandal to hit the secretive institution in three years.

Monsignor Lucio Angel Vallejo Balda, 54, who served on a special commission set up by Pope Francis to advise him on economic reform within the Vatican, was arrested along with a second member of the commission, Francesca Chaouqui, who has been dubbed a "sex bomb."

The Organization for Security and Cooperation in Europe (OSCE) charged in a damning report on Monday that Turkey's election was marred by a media crackdown, violence and other security concerns.

It said the campaign for Sunday's vote was characterized by "unfairness" and "fear" after a surge in violence.

Eight gunmen were killed and 18 others captured in Burundi after clashes with police outside the capital Bujumbura, police said Monday, the latest in months of violence in the troubled country.

The clashes with armed "criminals" took place in the rural Nyabiraba district, some 13 kilometers (eight miles) east of Bujumbura, police spokesman Pierre Nkurikiye said.

Pope Francis' visit to the violence-hit Central African Republic (CAR) remains "on the program," the Vatican said Monday, but the trip would have to be canceled if fighting in the capital intensifies.

"The pope's visit to CAR remains on the program. Francis greatly desires to go there," the Vatican's deputy spokesman Ciro Benedettini told AFP.

Germany on Monday welcomed Turkey's peaceful weekend election won by President Recep Tayyip Erdogan's party and urged his government to rule "in the spirit of national unity".

Chancellor Angela Merkel's chief spokesman Steffen Seibert praised the peaceful election process and high voter turnout, which he said proved "how deeply the Turkish people are invested in the democratic process".