An explosion in central Turkey tore through a bus carrying off-duty soldiers early Saturday, killing at least 13 people and wounding dozens in the second major attack targeting Turkey’s security forces in a week, authorities said. 

A military statement said the explosion, in the city of Kayseri, was caused by a car bomb. The 13 who were killed were soldiers on leave from the Kayseri Commando Brigade, the statement said; it added that civilians may have been among the injured. 

There was no immediate claim of responsibility for the explosion. It came a week after Kurdish militants carried out twin bombings at a soccer stadium in the heart of Istanbul that killed at least 44 people, an attack that signaled a sharp escalation of the decades-old conflict between the Turkish state and Kurdish separatist groups. 

Turkey’s deputy prime minister, Veysi Kaynak, told reporters the Saturday attack was similar to the explosions at the soccer stadium, which also involved a car bomb.

Turkish President Recep Tayyip Erdogan, in comments made after the bombing, pointed to “separatist terrorist organizations,” a reference to Kurdish militant groups, and called for a “national mobilization” to combat them. 

 Pictures of the aftermath of Saturday’s explosion showed the remains of the green-and-white bus, twisted and burned by the blast and surrounded by debris on a tree-lined street.  

Violence has accelerated since the collapse of a peace agreement in 2015 between the Erdogan government and the Kurdistan Workers’ Party, or PKK, leading to growing fears about the stability of Turkey, which is a NATO member and key ally of the United States. 

The country has suffered from spillover of the war in Syria and has faced attacks by Islamist militants. A failed coup attempt in July has been followed by a wave of domestic turmoil as the government has pursued a broad crackdown on its enemies, targeting those accused of fomenting the coup as well as standard political opponents. 

The intensification of the state’s conflict with the Kurds has been perhaps the most alarming turn, reviving memories of the bloody insurgency beginning in the 1980s that killed tens of thousands of people.

Authorities have arrested dozens of mainstream Kurdish political figures in recent months, and militant factions that reject any negotiations with the state have returned to the fore. They include a group called the Kurdistan Freedom Falcons, an offshoot of the PKK that claimed responsibility for the soccer stadium bombings and threatened to carry out more attacks.  

A pro-Kurdish political party, the Peoples’ Democratic Party, said at least ten of its offices in Istanbul and other cities were ransacked by unidentified people Saturday evening, although no injuries were reported. In a statement, the party blamed the authorities for the attacks, saying its calls for assistance had gone unanswered. “We know who is protecting and encouraging the attackers,” the statement said.