Police raided addresses across 21 provinces in an investigation led by prosecutors in Diyarbakir, the state-run Anadolu news agency reported. The southeastern city is the de facto capital of Turkey’s Kurds.

By mid-afternoon 126 suspects had been taken into custody, Anadolu said, although other media outlets said the tally had passed 150.

According to the government, the operation targeted the Kurdistan Workers Party (PKK), which has waged a 39-year war against the Turkish state that has cost tens of thousands of lives. The PKK is considered a terrorist organization by the United States and European Union.

Anadolu said those detained included the planners of dozens of public demonstrations since 2017 as well as those alleged to have provided support to the PKK through funding and propaganda.

Reuters, citing a security source, said simultaneous raids were conducted on 186 addresses after prosecutors issued arrest warrants for 216 people.

The timing of the operation ahead of the May 14 parliamentary and presidential elections, however, raised questions about whether the arrests were intended to curtail the People's Democratic Party (HDP), which has its roots in the Kurdish movement and is currently Turkey’s second-largest opposition party.

Emma Sinclair-Webb, Human Rights Watch’s Europe and Central Asia associate director, described the operation as “clearly an abuse of powers and [an] intimidation tactic before [the] election.”

In a statement, the HDP said the “detention frenzy” was designed to “steal the ballot box and the will of the people." It said, "This operation is a clear intimidation and threat to society and its political preferences.”

The statement went on, “It is no coincidence that lawyers who will protect the election ballot boxes, journalists who will inform the public and politicians who are competing with the [ruling Justice and Development Party] in the field have been targeted simultaneously.”

The HDP, which has seen thousands of its members, mayors and lawmakers imprisoned over the last eight years, faces legal pressure in an ongoing case seeking the HDP’s closure and a political ban on hundreds of its members. To sidestep such an outcome, the party is running parliamentary candidates under the umbrella of the little-known Green Left Party.

In a tweet sent via his lawyers, Selahattin Demirtas, the charismatic former HDP co-leader jailed since 2016, referred to a report that President Recep Tayyip Erdogan had recently sent a delegation to meet imprisoned PKK leader Abdullah Ocalan.

 “What do you think Erdogan wanted by sending a delegation to Imrali [prison]? When he couldn’t get what he wanted, he started accusing us of collaborating with 'terrorism' again,” Demirtas said.

During the 2019 local elections, a letter from Ocalan was reported by state media as calling for the HDP, which supported the opposition candidate, to remain “neutral” in a rerun of the vote in Istanbul.

Next month’s elections will be the biggest test Erdogan has faced in his 20 years in power. Rampant inflation driven in part by the president’s insistence on cutting interest rates have seen him drop in the polls. Criticism over the government's response to the February earthquakes, which highlighted deadly building practices, have exacerbated the challenge.

The Diyarbakir-based Lawyers’ Association for Freedom said many of its members had been detained. “We will not remain silent against the political operation against our association and other democratic institutions,” the association said.

The Diyarbakir Bar Association said 25 lawyers from the province as well as Batman, Mardin and Sanliurfa had been detained. “Considering the concerns regarding election security, we know there are intentions to intimidate with judicial threats against civil society organizations and rights defenders,” it said in a statement.

A confidentiality order had been put in place, the bar association said, limiting legal access and details about possible charges against detainees.

HDP joint deputy leader Tayip Temel said his co-deputy Ozlem Gunduz and members of the party’s central executive committee were detained. “As we approach the election, the government once again turned to detention operations out of fear of losing power,” he said.

The Long Live Our Theatre Initiative, meanwhile, said that 11 actors from Diyarbakir were detained.

Journalists from several southeast-based media outlets were also reportedly detained, including the owner and the editor of the Mezopotamya news agency, the editor-in-chief of  Yeni Yasam newspaper and the proprietor of Xwebun, Turkey’s only Kurdish-language newspaper. Police reportedly seized books and computers during searches of their homes.

Protests were held across several cities in response to the raids, from Izmir on the west coast to Van near the Iranian border.

In a separate development, Anadolu reported the killing of Mehmet Sari, who it said was a senior figure in the Kurdish People’s Protection Units (YPG), in Qamishli, northeast Syria. The YPG spearheaded the fight against the Islamic State in Syria but is considered a terror group by Ankara over its links to the PKK.

Anadolu said he was “neutralized” in an operation led by Turkey’s intelligence agency on April 14. Turkey has used drones to target YPG figures in recent months.