Turkey's appeals court upheld the conviction of a leading critic of President Recep Tayyip Erdogan, whose imprisonment has strained Ankara's relations with the West, Agence France-Presse reported.

Paris-born activist and philanthropist Osman Kavala was sentenced in April to life in prison without the possibility of parole on charges of trying to overthrow the government by funding street protests in 2013.

Anadolu news agency reported that an appeals court ruled that the April sentence was "in accordance with the law."

The defense can still appeal the case to Turkey's Supreme Court of Appeals.

Kavala's long-running trial has damaged NATO member Turkey's strategic but sometimes uneasy ties with its major Western allies since Kavala's surprise arrest in October 2017.

Kavala was then best known as a businessman who spent part of his fortune promoting culture and projects aimed at reconciling Turkey and Armenia.

Kavala was first charged with financing the 2013 wave of protests. A court acquitted him and released him in February 2020 - only to have police arrest him before he could return home to his wife.

Another court then charged him with involvement in an attempted coup against Erdogan in 2016. In the end, Kavala faced both sets of charges.

The U.S. said it was "deeply concerned" about the decision, and Germany demanded his immediate release.

Turkey has already ignored a ruling by the European Court of Human Rights recommending Kavala's release.