Police detain Sebahat Tuncel, co-chair of the pro-Kurdish Democratic Regions Party, during a protest in Diyarbakir, Turkey, against the arrest of Kurdish lawmakers on Nov. 4. (Sertac Kayar/Reuters)

Turkish President Recep Tayyip Erdogan sharply escalated his conflict with the Kurdish opposition on Friday as his government formally brought terrorism-related charges against at least eight members of parliament belonging to Turkey’s largest pro-Kurdish party, including the party’s two leaders.

The arrests, after chaotic nighttime raids on the homes of some of Turkey’s most prominent elected lawmakers, were criticized by Kurdish and human rights activists as a withering assault on Turkey’s democracy. They reverberated beyond the country’s borders, drawing condemnations from European capitals and the United Nations. And they threatened Turkey with greater instability, raising fears that the repression of the political party, the Peoples’ Democratic Party, or HDP, would empower militant Kurdish factions at war with the government.

As if to highlight the danger, a powerful car bomb exploded outside a police compound in the predominantly Kurdish city of Diyarbakir hours after the arrests, killing nine people and wounding more than 100, authorities said.

Erdogan’s government has been carrying out a broad crackdown on political opponents in the aftermath of a failed coup attempt in July, arresting or dismissing tens of thousands of people from their jobs.

They have included followers of Fethullah Gulen, an exiled Turkish cleric whom officials have blamed for the coup attempt. But the purge has spread well beyond his supporters and swept up thousands of others whom the government perceives as opponents, including journalists and academics.

Turkish police spray pepper gas as they arrest protesters on Nov. 4 in Ankara. (Getty Images)

In Washington, White House press secretary Josh Earnest said the Obama administration is “deeply disturbed” by the arrests of opposition lawmakers and has expressed its concerns to Turkey. U.N. Secretary General Ban Ki-moon and the European Union joined criticism of the detentions. Ban also condemned Friday’s car bombing.

The purge has coincided with heightened government anxiety over the growing assertiveness of Kurdish militant groups in Turkey and across the border in Syria, where Kurdish factions are allied with a U.S.-led coalition fighting the Islamic State.

Militants belonging to the outlawed Kurdistan Workers’ Party, or PKK, have stepped up attacks on Turkish security forces over the past year after a peace deal fell apart in 2015. That agreement had ended decades of war between Kurdish rebels and the Turkish state, which Kurds say has long persecuted their population. Ethnic Kurds make up nearly 20 percent of the country’s 75 million people.

The government has increasingly sought to link mainstream Kurdish opposition politicians to the militants, arresting local Kurdish leaders and shuttering pro-Kurdish institutions and media outlets.

In May, Turkey’s parliament voted to strip lawmakers of their immunity, including at least 50 HDP deputies who were facing investigation. Critics say Erdogan sought to remove opposition in parliament that would hinder his plans to establish a stronger presidency with expanded powers that would sideline the elected assembly.

But the government’s decision to move forcefully against the HDP — one of Turkey’s most formidable opposition groups and an avenue for the political integration of the country’s marginalized Kurdish minority — appeared to represent a turning point in the months-long campaign of arrests, analysts said.

The party, which holds more than 10 percent of the seats in parliament and is the chamber’s third-largest bloc, “represents 6 million votes,” said Cengiz Candar, a Turkish political analyst and visiting scholar at Stockholm University. Targeting the HDP, which includes the country’s most popular politicians, “was an invitation to civil strife — for partitioning the country,” he said.

Selahattin Demirtas and Figen Yuksekdag, co-leaders of the party, were ordered arrested pending trial. Six other lawmakers were also arrested on terrorism-related charges. Demirtas, a 43-year-old human rights lawyer, has a growing national and ­international profile and has emerged as a strong opponent of Erdogan.

Authorities said the HDP lawmakers were detained Friday after failing to answer an official summons to testify in a counterterrorism investigation. A statement from the Turkish prime minister’s office linked the detentions to Turkey’s “effective fight against terrorism.”

“There is no other country in the world which is fighting simultaneously against a minimum of 10 terrorist organizations like Turkey,” the statement said.

With the arrests, the government “has gone from talking peace with the PKK leader, and PKK commanders in the field, to going after anyone who is remotely advocating greater rights for the Kurds,” said journalist Amberin Zaman, a public policy scholar at the Wilson Center in Washington. “It is the same old notion — that Kurdish national aspirations can be crushed using military force,” she said.

At a news conference Friday in Istanbul, defiant HDP lawmakers accused Erdogan of attempting “to steer the country into a civil war.”

“Maybe in a few hours, none of us will be left,” HDP lawmaker Mithat Sancar said in reference to the speed and scale of the arrests.

But “they are mistaken if they expect us to bow down,” he said.

Overnight, as security forces detained the lawmakers, authorities blocked access to several social-media sites, according to the Internet monitoring group Turkey Blocks. The shutdown included Twitter, Facebook, YouTube, Instagram and the messaging service WhatsApp.

Users also reported Internet outages on mobile phones.

Videos of the police raids that circulated online included one showing Idris Baluken, a senior HDP leader, being led by ­uniformed officers to a waiting car.

“Don’t press my head!” Baluken yelled at an officer as they approached the vehicle.

“You will be held accountable for this,” he said. “I am the representative of hundreds of thousands of votes.”

Fahim reported from Cairo.