ISTANBUL/BERLIN - The Kurdistan Freedom Hawks (TAK) militant group on Thursday claimed responsibility for a suicide bombing in the Turkish capital Ankara that killed 37 people, and vowed to continue its strikes against security forces.Separately, Germany said it had closed its embassy in Ankara due to indications that an attack could be imminent. The consulate and German school in Istanbul were also closed, it said.TAK had previously claimed responsibility for car bombing in Ankara last month that killed 29 people. Ankara has now been hit by three bombings in a space of five months, ratcheting up security fears across the city and Turkey.In a statement posted online, the group described the car bombing, which occurred on Sunday, as revenge for security operations in the mainly Kurdish southeast that have been under way since July, in which hundreds of civilians, security forces and militants have been killed.TAK says it split from the Kurdistan Workers' Party (PKK). Experts who follow Kurdish militants say the groups retain ties. At least 40,000 people have been killed since the PKK began its fight for Kurdish autonomy in the southeast three decades ago.