Carnations are placed at the site of Sunday’s suicide bomb attack in Ankara, Turkey March 15, 2016. REUTERS/Umit Bektas

One police officer and three militants were killed in clashes between Turkish security forces and Kurdish insurgents in southeast Turkey’s largest city of Diyarbakir on Tuesday, security sources said, as local authorities imposed a curfew.

Fighting has renewed after 37 people were killed in an Ankara car bombing that security officials said involved two fighters, a male and a female from the Kurdistan Workers Party (PKK).

The PKK is listed as terrorist organization by Turkey, the United States and the European Union.

In response to the bombing, the Turkish military carried out air strikes on Monday and struck northern Iraq’s Qandil mountain area where the PKK’s main bases are, and the military said 45 PKK insurgents were believed to have been killed.

The strikes by F-16 and F-4 jets destroyed two weapons depots and two Katyusha rocket positions, the military also said in its statement on Tuesday.

One police officer and three militants were killed in the fighting in Diyarbakir’s Baglar district, the security sources said. A curfew was imposed in Baglar’s Kaynartepe neighbourhood from 3 a.m. (0100 GMT) in the face of moves by PKK militants to set up barricades, dig ditches and plant explosives in the area, local authorities said.

PKK fighters blocked roads and halted vehicles in the area and clashed with security forces sporadically through the night as a police helicopter flew overhead, witnesses said.

Speaking on Monday evening, Erdogan said the definition of terrorist needed to be broadened to include supporters.

“It may be the terrorist who detonates bombs and pulls the trigger, but it is these supporters who enable them to achieve their goals,” he said in a speech.

“Being an MP, an academic, journalist, writer or civil society group executive does not change the reality of that person being a terrorist,” he said.

Turkey’s predominantly Kurdish southeast has been witnessing a surge of violence since a 2-1/2 year ceasefire with the PKK collapsed in July. But the militants, who say they are fighting for Kurdish autonomy, have largely focused attacks on the security forces in southeastern towns, many of which have been under curfew.

A curfew was also declared on Monday in the southeastern town of Sirnak, alongside ones declared in Yuksekova, near the Iranian border and Nusaybin, near the Syrian border.

Turkey has been imposing curfews in several flashpoints in the southeast since August to root out militants linked to the PKK, who had set up barricades, dug trenches and planted explosives.

Last week, Turkey’s military terminated a three-month operation against the militants in the historic Sur district of Diyarbakir – the largest city in the country’s mostly Kurdish southeast. On Sunday, authorities eased the curfew in some streets and one neighborhood of Sur, but the siege over the district’s main areas was still in place.