The OSCE has denounced as "disgraceful" rocket strikes on a Ukrainian government-held port in Mariupol that killed 30 people shortly before pro-Russian insurgents announced the launch of a major new assault.
The pan-European security group charged with observing the conflict said its Ukrainian mission leader viewed "the shelling in Mariupol ... as a reckless, indiscriminate and disgraceful attack aimed at a heavily-populated residential area whose victims included women, children and the elderly".
The local mayor's office said 97 people were also wounded in the Sea of Azov port of nearly 500,000 by Grad rockets that smashed into a packed residential district early in the morning and then again shortly after midday.
"This dangerous situation can't continue," the Organisation for Security and Co-operation in Europe's Mission Chief Ertugrul Apakan said in a statement.
"We need an immediate ceasefire. Ukraine and its people need and deserve peace. The parties must return to the negotiating table without further delay and implement fully the Minsk agreements," Mr Apakan added.
On Friday rebel leader Alexander Zakharchenko announced his withdrawal from all truce talks with the pro-Western leaders in Kiev, who rose to power in the wake of the February ousting of a Russian-backed president.
Mr Zakharchenko stated his forces had launched "an offensive against Mariupol" but did not accept direct responsibility for the earlier rocket attack.
He called the strategic industrial port's potential capture "the best tribute possible for all our dead".
