The summit will come just a day after a meeting of Ukrainian, Russian, French and German leaders at what is seen by some as the final attempt to reach a cease fire in Ukraine.

The STA learnt from undisclosed sources that the summit is to voice a reserved welcome if a cease fire will be reached; in the opposite case the leaders will call for additional measures.

Slovenia's prime minister has told the STA that the crisis in Ukraine should be resolved through dialogue. He believes the EU should find a way to continue promoting a peaceful solution.

Talking to the STA over the phone during a visit to Luxembourg on Wednesday, Cerar also said that he was looking forward to meeting Tsipras and added that "solidarity to Greeks and other European citizens" needs to be preserved.

But Cerar also pointed out that "accepted European rules and standards need to be respected", which requires seeking solutions for Greece "within the framework of the rules."

As regards the fight against terrorism, the EU leaders are expected to call for the contentious exchange of passenger name records (PNR). The debate is however expected to focus on the consolidation of the Schengen border.