Police raid homes of co-chairmen of Peoples’ Democratic Party; government accuses them of defying subpoenas to testify in connection with terrorism-related charges

Selahattin Demirtas, right, the co-chairman of the pro-Kurdish Peoples’ Democracy Party, was detained after police raided his home in Diyarbakir in the early hours of Friday. The party’s popularity has soared under the leadership of Mr. Demirtas, who has emerged as a formidable challenger to the president.

Turkish authorities detained the leaders of the country’s pro-Kurdish party in the early hours of Friday, launching a crackdown that threatens to crush one of the country’s biggest opposition parties.

Police raided the homes of Peoples’ Democratic Party co-leaders Selahattin Demirtas and Figen Yuksekdag and took them into custody for defying subpoenas to testify in connection with terrorism-related charges, according to party and state officials.

At least 11 lawmakers from the party, known as HDP, were also detained in the post-midnight operations, the Interior Ministry said. The police descended on HDP headquarters in Ankara, where party members resisted search warrants and arrests, chanting “We have no deputies to give up,” videos posted on the party’s official Twitter account show.

“They came at midnight and took Yuksekdag by force—those who raided our headquarters, took away our deputies, also forcefully swept away Demirtas from his house,” the HDP said in a Twitter post.

Turkey’s government has been calling on the judiciary to bring HDP to account for its alleged support of terrorism.

“The defendants are being detained for questioning, following their insistent defiance of prosecutors’ invitation to testify and violation of the law,” the prime minister’s office said in a statement.

The detentions mark the government’s most significant step yet against pro-Kurdish politicians since it began a sweeping crackdown in response to the failed coup attempt in July. The government initially focused on the network of U.S.-based Turkish imam Fethullah Gulen, whom President Recep Tayyip Erdogan accuses of masterminding the putsch, but then quickly expanded its campaign to all terrorist threats, including the Kurdish insurgency.

Mr. Erdogan and his government accuse elected HDP officials of supporting the Kurdistan Workers’ Party, or PKK, which is listed as a terrorist organization by Turkey and its North Atlantic Treaty Organization allies. The PKK has fought for Kurdish autonomy in southeast Turkey since 1984 in a conflict that has killed more than 40,000 people.

HDP officials deny having links with or supporting the PKK.

Friday’s detentions mark Mr. Erdogan’s biggest effort yet to quash Turkey’s strengthening Kurdish political movement.

In May, Mr. Erdogan’s deputies, joined by nationalists and some secularist opposition lawmakers, stripped almost all of the pro-Kurdish representatives’ immunity, paving the way for them to face terrorism-related charges.

But HDP lawmakers, led by Mr. Demirtas and Ms. Yuksekdag, defied prosecutors’ demands that they testify, accusing the government of seeking to undermine elected officials and civilian politics amid a surge in violence.

Authorities last week ousted the elected HDP mayor in the Kurds’ de facto capital in Turkey, Diyarbakir, and appointed a trustee to run the city.

The HDP won more than 10% of the votes in early elections last November, becoming the third-largest of the four parties in parliament. The party’s popularity has soared under the leadership of Mr. Demirtas, who emerged as a formidable challenger to check Mr. Erdogan’s expanding power.

That helped the HDP double its support to 13% of the vote in June 2015 elections and denied the president’s party a ruling majority in parliament for the first time since 2002.