An Istanbul court has acquitted 26 people charged with offences including formation of a criminal group for their role in organising protests in 2013 against the government of Turkish President Recep Tayyip Erdogan.

The 26 suspects were all leaders of Taksim Solidarity, an umbrella group of civil society, union and political groups that was at the forefront of the demonstrations.

The activists, including doctors, architects and engineers, had been charged with setting up a crime syndicate, violating public order and organising illegal protests through social media. 

The court ruled on Wednesday that there was insufficient evidence to convict the defendants, five of whom faced up to 30 years in prison, lawyer Can Atalay told the Reuters news agency.

Amnesty International, the UK-based rights group, had described the trial as scandalous.

Taksim Solidarity organised the protests on Istanbul's Taksim Square in late May 2013 in a bid to prevent authorities from demolishing a park there and express frustration with the ruling AK Party, now in power for more than 12 years.

Erdogan was prime minister at the time and described the protests, which escalated to violent clashes after police broke up the peaceful demonstration, as the work of "riff-raff."

Critics said his response reflected an increasing intolerance of opposition. He has since been elected president.

Hundreds of other people are still being prosecuted in trials around the country for alleged crimes related to the protests, the biggest challenge the AK Party had seen since taking office.

At least six people died in clashes with police.

Erdogan hopes the AK Party will win a two-thirds majority in June's parliamentary election, allowing the government to change the constitution and endow the presidency, now a largely ceremonial post, with strong executive powers.

Source: Agencies