Police in Turkey have confronted a group of supporters of the Peoples’ Democratic Party’s (HDP) in Istanbul, preventing them from joining a march by the country’s biggest pro-Kurdish party.

The “Conscience and Justice” march was underway on Sunday, when law enforcement forces attacked participants with tear gas canisters and rubber bullets, AFP reported.

The demonstrators demanded the release of HDP parliamentarians and journalists.

The HDP is Turkey’s second-largest opposition party after the Republican People’s Party (CHP). It has come under increasing pressure since the government launched a crackdown on the outlawed anti-Ankara Kurdistan Workers’ Party (PKK) in the country’s southeast two years ago.

The party says thousands of its supporters have been arrested since the onset of the government campaign.

The government says it has killed thousands of the militants since the launch of the operation. The HDP contests the claim, saying many of the fatalities are civilians.

Ankara has also imposed bans and prison sentences on four of the party’s parliamentarians, accusing them of links to “terror” organizations, including the PKK. The party denies having any links with the separatist militants.

The party is also critical of the administration’s ongoing sweeping crackdown on the people it accuses of links to Fetullah Gulen. Ankara says the US-based cleric masterminded a failed July 2016 coup against the government.

Thousands have been either imprisoned or dismissed from their jobs during the operations, in what is seen as, the authorities’ intolerance of all dissent.