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Five people were reported to have been injured when a pipe bomb exploded on an overpass near a metro station in Istanbul yesterday

Some train operations were halted during the evening rush hour as a result of the blast near the Bayrampasa station.

The explosion heightening security fears in Europe’s biggest city.

Turkey has been on high alert since more than 100 people were killed and 180 injured by two suicide bombers in the capital Ankara in October, three months after a similar attack at a town near the Syrian border in July left 33 dead.

The Foreign and Commonwealth Office continues to warn of a “high threat” of terrorism in Turkey with British travellers advised to be vigilant.

Turkish national police guards were targeted by gunfire outside Dolmabahçe Palace in Istanbul in August 19 while two people opened fire outside the US Consulate in the city nine days earlier.

There were reports of possible threats to public transport in Istanbul, in particular the metro stations at Yenikapi, Taksim, Osmanbey and Haciosman and stops on the Metrobus line in July, according to the FCO.