Ukraine has been shaken by an attack with left at least 20 civilians dead, according to local media.
The series of rocket attacks left 27 people dead and many others injured in the eastern city of Mariupol. The Ukranian national forces and pro-Russian rebels continue to accuse each other to be responsible for the attack.
Meanwhile, East Ukrainian rebels have launched an offensive on the city of Mariupol, one of their leaders says, as rockets kill and injure dozens in the port city. Ukraines Prime Minister Arseniy Yatsenyuk called for an urgent session of the UN Security Council to discuss, what he says, is Russias role in the conflict in eastern Ukraine.
US Secretary of State John Kerry said he joined his European counterparts in condemning an assault by pro-Russian separatists on Mariupol, Ukraine, and he called on Russia to end its support for the rebels.
"It is reprehensible that the separatists are publicly glorifying this and other offensives in blatant violation of the Minsk agreements they signed," Kerry said in a statement issued while on a visit to Zurich.
He said the separatists' assault has been aided by Russia's "irresponsible and dangerous decision to resupply them in recent weeks with hundreds of new pieces of advanced weaponry, including rocket systems, heavy artillery, tanks, armored vehicles, in addition to continuing operational command and control."
"We call on Russia to end its support for separatists immediately, close the international border with Ukraine, and withdraw all weapons, fighters and financial backing. Otherwise, US and international pressure on Russia and its proxies will only increase," Kerry added.
Ten people have been killed in shelling by pro-Russian separatists of the east Ukrainian port city of Mariupol, the head of the Kiev-controlled Donetsk regional police said.
As a result of shelling by rebels of a residential sector of Mariupol ... ten people have been killed.
A mortar shelling of a bus stop in Ukraine was a "crime against humanity", the Russian Foreign Ministry has said.
In a statement, the ministry denied any involvement in the attack, which killed at least eight civilians in Donetsk, and blamed it on Ukrainian troops.
We regard this incident as a crime against humanity - blunt provocation aimed at undermining efforts to seek a peaceful solution of the Ukrainian crisis.
Ukraine's Prime Minister Arseny Yatseniuk blamed separatist rebels for the attack, and said Russia bore responsibility.
Russia should bear responsibility for a deadly mortar attack on a trolleybus which killed a number of passengers, Ukraine's Prime Minister has said.
At a ceremony to mark Unity Day in Kiev, Arseny Yatseniuk blamed pro-Russian rebels for the attack at a bus stop in Donetsk, saying at least eight people had died in the blast.
Previous reports suggested up to 13 people had died.
Today Russian terrorists again committed a terrible act against humanity. Russia bears responsibility for this.
At least seven civilians were killed as a shelling mortar attack targeted a bus stop in Ukraine just as a trolleybus pulled up.
Earlier reports suggested as many as 13 people had been killed in the blast, in the south of the rebel-held city of Donetsk, but officials have yet to confirm the death toll.
A number of people were killed aboard the bus, while images from the scene show the bodies of passing pedestrians lying in the street.
Nearby cars could be seen completely burned out in the attack, while the windows of nearby shops and buildings were blown out.
Unconfirmed reports from eye-witnesses suggested the blast may have originated from one of the cars.
We heard the blast and ran here. And here we saw the bus is destroyed, the car has exploded, lots of dead bodies.
There was a wounded man on a bus, he was asking for help. There also was a dead body laying behind us and lots and lots of wounded.
Thirteen people have been killed in a shelling at a tram stop in Donetsk, Ukraine, Agence France-Press reports, citing sources at city hall.
Diplomats have moved closer to establishing security zones between pro-Russian fighters and Ukrainian forces, German Foreign Minister Frank-Walter Steinmeier has said.
The four-way talks between the foreign ministers of France, Germany, Russia and Ukraine made "perceivable progress" during their meeting in Berlin, Steinmeier said.
He added that an agreement was reached on a demarcation line from which heavy weaponry had to be withdrawn.
Talks aimed at reaching a stable ceasefire in Ukraine between its government forces and pro-Russian armed groups ended after more than five hours.
There was no indication of progress, and questions about when the next round might take place.
The opening session occurred in the Belarusian capital Minsk, a day after Ukraine's decision to drop its non-aligned status, which added a new element of tension to the attempts to resolve the violent crisis in the country.
The talks were to discuss how to improve an often-violated ceasefire that was declared in September, to pull back heavy weapons and to exchange of war prisoners.
The negotiators included representatives of Ukraine, Russia, pro-Russia rebels and the Organisation for Security and Co-operation in Europe.
News media were not allowed access to the meeting and the participants left the session without comment.
Another round had been tentatively set for tomorrow, but the Belarusian foreign ministry said after the session's conclusion that it was unclear if that would take place.
Vladimir Putin has accused Nato countries of "building a new Berlin wall" and blamed other nations for the current situation in eastern Ukraine.
The Russian President said Moscow was ready to mediate in the crisis in a bid to resolve it politically, rather than militarily.
When asked by a Ukrainian journalist how many Russian soldiers had been sent into the region, Putin denied sending any - claiming any that went did so of their own volition.
He also said the current economic crisis in Russia was not a penalty for its involvement in Crimea, claiming sanctions were an attempt to turn Russia from a bear with "claws" into a stuffed animal.