ATHENS - Greece's new Popular Unity party of far-left rebels from the leftist Syriza party will seek a mandate to form a government as the third-biggest group in parliament, a senior party lawmaker told Reuters on Friday.

Twenty-five anti-bailout rebels from Syriza broke away to form the party on Friday.

Under Greece's constitution, the three biggest parties in parliament are given a three-day mandate to form a government following the resignation of Alexis Tsipras as prime minister.

The conservative New Democracy party currently has the mandate, which would pass to the next group if it was unsuccessful in its effort.

"We will take the mandate and we will utilize it," said Dimitris Stratoulis, a lawmaker with the Popular Unity party.