A crowded open-air market and nearby homes in Ukraine's strategically important coastal city of Mariupol came under rocket fire Saturday morning, killing at least 16 people, city authorities said.
Mariupol lies on the Azov Sea and is the major city between mainland Russia and the Russia-annexed Crimean Peninsula. Heavy fighting in the region in the autumn raised fears that Russian-backed separatist forces would try to establish a land link between Russia and Crimea.
Rebel forces have positions within six miles from Mariupol's eastern outskirts.
The Interior Ministry said rockets struck homes, setting them alight, as well as the market and shops. A Ukrainian military checkpoint on a road leading out of the city toward rebel-held areas was also hit, police said. Mariupol city council said that 74 have been hospitalized for their injuries.
Rocket strikes on Mariupol come as separatists have declared their intention to mount a multi-pronged offensive aimed at vastly increasing the territory under their control. That would definitively upend recent European attempts to mediate an end to the fighting.
The city council urged residents not to panic and to ignore rumors that Ukrainian armed forces were planning to withdraw from Mariupol.
"On the contrary, all units are on fully battle-ready. Security measures in the city have been strengthened," the council said in a statement.
No armed separatist units have been noted moving toward the city, the statement added.
The U.N. human rights agency on Friday raised its estimate of the conflict's overall death toll to nearly 5,100 since April.
On Thursday, mortars rained down on the center of the separatist stronghold of Donetsk, hitting a bus and killing several bystanders. Rebel officials said 13 were killed in that attack. Monitors from the Organization for Security and Cooperation in Europe cited city morgue officials as saying they have received eight bodies.
On Jan. 13, a bus parked near an army checkpoint north of Mariupol was hit by a shell, resulting in the death of 13 people. Ukraine blamed the rocket attack on separatists.
The OSCE's special monitoring mission (SMM) in east Ukraine on Saturday expressed concern over the growing number of civilian casualties and called for restraint from all sides.
"The SMM strongly condemns the continuation of the fighting in residential areas. Using residential areas as firing positions attracts counter-firing to these areas, further endangering the lives of civilians," the mission said in a statement.
Clashes are taking place across the eastern regions of Donetsk and Luhansk, where separatist insurgencies emerged in April following Russia's annexation of Ukraine's Crimean Peninsula.
Fighting has also been intensifying recently for the government-held town of Debaltseve. Main roads to the town lie in separatist control and speculation is mounting that Ukrainian forces stationed there could soon be fully encircled.
Russia insists that it does not support the rebels, but Western military officials say the sheer number of heavy weapons under rebel control belies that claim.
A peace deal signed in September in the Belarusian capital of Minsk envisaged a cease-fire and a pullout of heavy weapons from a division line in eastern Ukraine. It has been repeatedly violated by both sides, and heavy artillery and rocket barrages have increased the civilian death toll in the last few weeks.
Foreign ministers from Russia, Ukraine, France and Germany agreed Wednesday to revive that division line, but fighting has continued unabated.