Latest from our news desk on the Istanbul subway bomb:
An explosion near an Istanbul subway station has caused some injuries, Turkish media are reporting.
The cause of the explosion on an overpass of the central Bayrampasa station is still unknown.
District Mayor Atilla Aydiner said the blast occurred during rush hour and that five people were injured near the station, where the subway cars run above ground.
Aydiner said the blast could have been caused by a pipe bomb.
But Istanbul city officials said the blast could have been caused by an electrical transformer.
Istanbul's entire subway system was closed after the blast but it has since reopened.
Istanbul is Turkey's largest city with a population of some 15 million people.
The country has been on high alert since October, when more than 100 people were killed by two explosions during a peace march in the capital, Ankara. (AP, AFP, TASS)
AP has more details on the explosion in Istanbul, which a local mayor and police sources have said was caused by a bomb and which wounded five people.
The bomb was left on barriers on the overpass, said Atilla Aydiner, the mayor for Istanbul's Bayrampasa district. Earlier, Istanbul's governor said one person was slightly injured in the blast.
The explosion occurred at 1530 GMT (10:30 a.m. EST) at an overpass near the city's Bayrampasa subway station, on the European side of Istanbul. Several ambulances and police vehicles were sent to the area.
The Dogan news agency said it was a hand-made cluster bomb. Dogan also obtained closed-circuit TV footage showing an explosion looking like a firework display in the night sky. The agency's footage also showed a white van on the overpass, with large holes in its windshield, apparently damaged in the explosion. The Anadolu Agency identified an injured person as a 36-year-old man and said he wasn't in serious condition. It wasn't immediately clear if he was in the vehicle at the time of the explosion.
'Turkish Stream, Akkuyu Nuclear Plant Not Frozen'
The Turkish Stream project and the Akkuyu Nuclear Power Plant project have not been frozen as part of Russian trade sanctions on Turkey, Minister of Economic Development Alexey Ulyukaev has said.
"As far as major investment projects are concerned, so far there has been no decision about freezing them or stopping their funding. Therefore we presume that they will operate just as they did before the government adopted this decision," Ulyukaev said.
Ulyukaev's comments followed earlier reports by Reuters and TASS that the Turkish Stream gas pipeline project could be frozen.
The Akkuyu nuclear power plant is under construction in Turkey.
The Mayor of Istanbul's Bayrampasa district is also saying that the explosion in a local metro station was caused by a bomb.
Turkish security sources are now saying that a hand made bomb caused the explosion in an Istanbul metro station this afternoon.
'Russia, Turkey To Freeze Talks About Turkish Stream Project'
Russia and Turkey are to suspend discussions about the Turkish Stream gas pipeline project in the wake of the Russian government's freezing of the work of the joint Russian-Turkish Intergovernmental Commission, a source familiar with the negotiations has told the TASS news agency.
Russia's Energy Ministry and Russian gas giant Gazprom have so far refused to comment, TASS reports.
However, two Gazprom sources told Reuters earlier today that Russia may freeze work on the Turkish Stream project, which is intended to pump gas from Russia via Turkey into southeastern Europe, bypassing Ukraine.
"We're expecting that the head of state, in all likelihood, could declare a freezing of Turkish Stream, or at least some kind of timeout should be announced," one Gazprom source told Reuters on condition of anonymity.
One person has been killed and several others wounded at the explosion at a metro station in Istanbul, Turkey. There appears to be some uncertainty about the cause of the blast.