By Renee Maltezou and George Georgiopoulos ATHENS (Reuters) - Rebels angered by Greece's international bailout walked out of the leftist Syriza party on Friday, formalising a widely-expected split after leader Alexis Tsipras resigned as prime minister to pave the way for early elections. The new anti-bailout Popular Unity party set up by the far leftists is expected to steal some anti-euro voters away from Tsipras. The split - which cost Tsipras 25 lawmakers or a sixth of Syriza's parliamentary group - came a day after he abruptly resigned to force early elections in a bid to cement his grip on power and deal with the growing rebellion in the party's ranks.