Mogherini convened an urgent meeting of members' representatives gathered in Ulan Bator, who "expressed support to the democratic institutions of the country and condemned the use of violence against them", the EU said in a separate statement. 

"They agreed that any escalation of violence involving civilians has to be avoided," it added. 

NATO and US President Barack Obama have also backed the country's democratic institutions following the coup attempt.

Brussels will be watching with deep concern the events in Turkey, a key partner on its southeastern flank which has been trying to join the EU for many years without success.

Turkey is also a crucial partner for the EU because of the controversial deal they signed in March to tackle the migration crisis.

Under the deal, Ankara agreed to take back migrants and refugees from the Greek islands and to stop people crossing the Aegean Sea. In return it is to get aid and visa-free travel for 80 million Turks to the EU.

The bloc overcame its aversion to Erdogan's increasingly authoritarian rule, which has received sharp criticism from the EU, to sign the deal.

Turkey will now likely dominate an EU foreign ministers' meeting on Monday which will also be attended by US Secretary of State John Kerry. (AFP)