CNN could not confirm 12 deaths, but its team in Donetsk saw seven bodies after a series of shell blasts near the center of the city.
Five bodies, concealed under sheets, could be seen at a spot by the Hotel Europe, where a local billionaire has organized food aid handouts by his staff. One man had died at the wheel of his car. A shell apparently hit near where dozens of people were waiting in line for much needed supplies.
Elsewhere, two more bodies could be seen where a trolley bus was hit.
Until now the fighting has largely been concentrated on the outskirts of the city, near the airport.
But Friday, the blasts moved significantly closer to the city center, where there are no obvious military targets.
It's not clear who is responsible for the shelling. In previous instances, each side has blamed the other.
What is clear is the mounting civilian death toll, with the ordinary residents of Donetsk being caught up in the fighting.
'Countless rockets' fired
Last Saturday, at least 30 civilians were killed in shelling in the southeastern city of Mariupol, while eight people died when a transit stop in Donetsk was shelled two days earlier.
There has been fierce fighting around the town of Debaltseve, northeast of Donetsk, where separatist forces have almost surrounded Ukrainian troops.
U.S. State Department spokeswoman Jen Psaki condemned the fighting there in remarks Thursday and pointed the finger firmly at the pro-Russian rebels for any casualties.
"Over the past week, the separatists have fired countless rockets at the city, killing and wounding scores of innocent people, and prompting the Ukrainian government and local NGOs to organize a citywide evacuation," she said.
"There can also be no mistake about Russia's role in the escalation of violence, which is causing suffering and death among those Russia has claimed it wants to protect."
The government in Kiev and its Western allies accuse Russia of fueling the violence by sending troops and military equipment over the border into Ukraine. Moscow denies the allegation, although it has said some Russian soldiers are fighting in Ukraine as volunteers.
'Black year' for security
Presenting his annual report Friday at NATO headquarters in Brussels, Belgium, Secretary General Jens Stoltenberg said 2014 had been a "black year" for European security.
Russia is following a "disturbing pattern," he said, "using military force to annex Crimea, destabilize eastern Ukraine and intimidate its neighbors" in disregard of international law.
On Thursday, the European Union Foreign Affairs Council announced it was extending the financial sanctions imposed against Russian and Ukrainian separatist interests until September in response to the mounting violence. It will also decide whether to add more names to the list of those sanctioned when it meets February 9.
EU foreign policy chief Federica Mogherini said she was pleased the European Union was maintaining a united front on the issue.
"We hope this can help put pressure, in particular on Russia, to take positive steps and prevent negative steps to you've seen in recent days," she said.
In a statement, the council strongly condemned "the indiscriminate shelling of the residential areas, especially in Mariupol and the recent escalation of fighting in the Donetsk and Luhansk regions of Ukraine."
It said it was shocked by the high number of casualties, adding: "It notes evidence of continued and growing support given to the separatists by Russia, which underlines Russia's responsibility."
There are now 900,000 internally displaced people and 600,000 refugees as a result of the conflict, the council said. The EU has already given 95 million euros for humanitarian assistance, it said.
Russia's Foreign Ministry said Friday that it was "disappointed" by the council's decision on sanctions and accused it of bias in favor of Kiev, saying it was hostage to an "aggressive minority" that is opposed to Russia.
"It's time for the European Union to realize the futility of the sanctions standoff that only hurts people and our economies," the ministry said in a statement.
Ukrainian President Petro Poroshenko announced Monday
that Kiev would ask the Hague tribunal to investigate alleged "crimes against humanity" in the conflict in eastern Ukraine.
The conflict broke out last spring after Russia annexed Ukraine's southeastern Crimea region and as pro-Russia separatists claimed control of the Luhansk and Donetsk regions. A ceasefire agreed to in Minsk, Belarus, in September crumbled long ago.
New talks were supposed to be taking place in Minsk, aimed at finding a political solution to the crisis, but there are conflicting reports as to whether they had been delayed.
The new talks were unlikely to happen because representatives for Ukraine's government had not arrived Friday, even though rebel representatives were there, said Eduard Basurin, the self-declared defense minister for the rebel group Donetsk People's Republic.
From mid-April to January 21, the conflict killed at least 5,086 people and injured at least 10,948 others, according to the United Nations.