ISTANBUL (Reuters) - Turkish police detained three district heads of the pro-Kurdish Peoples’ Democratic Party (HDP) and seven others in Istanbul on Friday over alleged links to militants, police said, two days after a court case began over banning the party. Separately, Turkey’s Human Rights Association (IHD) co-chairman Ozturk Turkdogan was arrested by police at his home, IHD said, prompting human rights groups to call for his release. Turkdogan was then released on Friday evening, the association said. A prosecutor filed a case with the Constitutional Court on Wednesday demanding a ban on the HDP, the culmination of a years-long crackdown against parliament’s third-largest party. The HDP called it a “political coup”. State-owned Anadolu news agency said on Friday that police arrested the 10 people over alleged links to Kurdistan Workers Party (PKK) militants - deemed a terrorist group by Turkey, the European Union and the United States. Prosecutors have ordered 12 arrested in total, including former provincial heads of the HDP, it said. Media reports said Turkdogan was detained as part of those raids. Human Rights Watch Turkey director Emma Sinclair-Webb called for his immediate release on Twitter, addressing the country’s foreign and justice ministers. “In Brussels you talk about dialogue with civil society but the reality at home is dawn raids and arrest of human rights defenders,” she said. European Council President Charles Michel is scheduled to hold a video conference with President Tayyip Erdogan and European Commission head Ursula von der Leyen on Friday. EU leaders are then due to discuss strained ties with Turkey at a summit next week. Police in Istanbul staged raids in four areas and detained two top HDP officials in the district of Kagithane as well as its Besiktas district head among 15 suspects sought, the city’s police headquarters said. Erdogan unveiled a “human rights action plan” this month, saying Ankara would strengthen the right to a fair trial and the right of freedom of expression. Critics say the plan fails to tackle an erosion of human rights in the country, however.