A gunman has opened fire at Turkish journalist Can Dundar, who is standing trial in Istanbul on charges of revealing state secrets, the BBC News reported. 

The assailant fired at least three shots outside the court, eyewitnesses said. Dundar escaped unharmed but a reporter was reportedly injured.

Police say they have arrested the suspected gunman. Erdem Gul, a former colleague of Mr Dundar who is also on trial, said the attacker shouted "traitor" as he fired.

Dundar, a former newspaper editor, was briefing reporters outside the courthouse when the incident occurred. 

He is standing trial alongside Gul over a series of reports in Cumhuriyet newspaper that alleged Turkish intelligence operatives were transporting weapons to Syria in early 2014.

Both journalists face life in prison if convicted. 

Turkey's President Recep Tayyip Erdogan has faced international criticism over the decision to prosecute the two journalists.

They are among a number of journalists and human rights activists who have been detained or prosecuted in Turkey in recent months.