A Turkish court has sentenced an activist and philanthropist to life in prison in a case Turkey's international allies said was politically motivated.

Osman Kavala has already spent more than four years in prison without being convicted.

He was found guilty of charges related to the nationwide protests in 2013 and the failed coup attempt in 2016.

Kavala denied the charges and has accused the government of "judicial assassination".

The United States said it was "deeply troubled" by the conviction.

Western diplomats were among those attending a packed court.

Kavala was first accused of orchestrating and financing nationwide anti-government protests that erupted in 2013.

He was acquitted, but soon after he was accused of being part of the attempted coup in 2016, which saw tens of thousands of people jailed or lose their jobs.

At the trial, he was charged with both counts.

Europe's top court, the European Court of Human Rights, has said there was insufficient evidence he committed an offence, and that his arrest was an attempt to "silence him and dissuade other human rights defenders".

"His unjust conviction is inconsistent with respect for human rights, fundamental freedoms, and the rule of law," the US State Department said in a statement.

Kavala was born in Paris and educated in the UK. Before being thrust to prominence, he ran a cultural centre.

Recep Tayyip Erdogan, whose government has become more authoritarian in recent years, has accused Kavala of being an agent of the Hungarian-born US billionaire George Soros.