File Photo: Ukraine's President Petro Poroshenko. (Reuters)
Ukrainian President Petro Poroshenko said on Sunday that he saw "no alternative" to a September truce with separatist rebels, after a weekend rocket assault that killed 30 people in a government-held city.
"Ukraine remains a firm proponent of a peaceful solution," Mr Poroshenko told an emergency Ukrainian National Security and Defence Council meeting.
"We see no alternative to Minsk," he added in reference to the Belarussian capital where the often-broken September 5 ceasefire agreement was signed.
Saturday's rocket assault on the government-held port of Mariupol came a day after rebel commander Alexander Zakharchenko pulled out of all future peace talks with the pro-Western government in Kiev.
Mr Zakharchenko announced the launch of a new offensive aimed at capturing Mariupol and other eastern lands allegiant to Kiev a few hours after the attack.
But he later denied ordering an all-out invasion of the Sea of Azov port of nearly half a million and his deputy rejected responsibility for the civilian deaths.
Mr Poroshenko said the European Union would hold a meeting of its foreign ministers on Monday at which Kiev would lobby for still firmer sanctions against Russia for its alleged military and financial backing of the rebel campaign.
He said that Ukraine and the 28-nation bloc "will coordinate steps for improving Ukraine's security and upping the pressure on Russia."
Moscow denies sending troops and weapons in to the war zone and calls NATO satellite imagery purporting to show its troop movements in eastern Ukraine forgeries designed to discredit Russian President Vladimir Putin.