Turkish opposition leader Figen Yüksekdağ | AFP via Getty Images EU ‘extremely worried’ over Turkey opposition arrests The MPs face terror charges.

Turkish opposition leaders Figen Yüksekdağ and Selahattin Demirtaş were arrested early Friday, the country's state-run news agency Anadolou reported.

The People's Democratic Party (HDP) co-chairs were taken into custody for failing to respond to a summons to provide testimony in a probe by the chief prosecutor of Diyarbakır, in southeastern Turkey.

Both Yüksekdağ and Demirtaş face charges of terrorism under the country's anti-terror laws, after their parliamentary immunity was lifted in May.

Police searched the HDP's head offices in Ankara and arrested at least nine other MPs from the HDP party, according to the BBC. The government claims the party has links to the Kurdistan Workers' Party (PKK), a militant group deemed a terrorist organization by the United States, the European Union and Turkey. HDP denies any connection to the group.

The EU was "extremely worried" about the arrests, the bloc's foreign affairs chief Federica Mogherini tweeted Friday, adding she had been in touch with Ankara.

Extremely worried for arrest of @hdpdemirtas & other @HDPgenelmerkezi MPs. In contact w/ authorities Called EU ambassadors meeting in Ankara — Federica Mogherini (@FedericaMog) November 4, 2016

President of the European Parliament Martin Schulz said in a statement Friday afternoon: "With this latest string of detentions ... Turkish authorities are not just pushing Turkey further away from democracy, but they are also turning their backs on the values, principles, norms and rules underpinning EU-Turkey relations."

HDP an essential element of #Turkey democratic life. Detention of HDP leaders @hdpdemirtas @FigenYuksekdag a blow to pluralism & democracy — EP President (@EP_President) November 4, 2016

The arrests are part of a wider crackdown orchestrated by Turkish President Recep Tayyip Erdoğan's government. Since the attempted coup in July, thousands of civil servants, academics, journalists, police and members of the military have been arrested.

Ertuğrul Kürkçü, an HDP MP who is currently abroad, told the BBC the detentions were "totally unlawful" and said the crackdown had "nothing to do with procedural law, criminal law, any law whatsoever or the constitution."

A few hours after the arrest, a car bomb went off in Diyarbakır, near the police station where the HDP leaders were being held, killing one person and wounding at least 30 others, according to media reports. The provincial governor's office wrote in a statement that the PKK party was believed to be responsible for the blasts.

This story was updated with comments from Martin Schulz.