Pro-Russia militants in eastern Ukraine on Saturday released seven European military observers as the Ukraine government pressed ahead with a military offensive to take back control of cities from the militancy.
Military observers from the Organization for Security and Cooperation in Europe were held for more than a week on what militants said were charges of spying. The OSCE is a diplomatic group, and said its members were grabbed as bargaining chips.
U.S. Secretary of State John Kerry said the release was a step in the right direction. But he pressed Russia to stop backing separatists and to help oust them from government buildings seized in about a dozen cities and towns.
Kerry talked to reporters after speaking with Russian Minister Sergey Lavrov while flying from Ethiopia to Congo.
"We will both advance ideas about how to do that without any promises of what those possibilities may produce," Kerry said.
President Obama has threatened to impose more financial sanctions on Moscow if it does not stop assisting the militancy, but Florida Senator Marco Rubio said Saturday that Obama has failed to take strong enough action to alter the situation
"President Obama talks tough about Vladimir Putin. But his actions have not gone far enough to change Putin's calculation that the benefits of his aggression outweigh the costs," Rubio, a Republican, said.
Senate Republicans have introduced a bill that would increase sanctions and provide Ukraine with defensive military assistance, something Obama has refused to do.
Meanwhile, Interior Minister Arsen Avakov said Ukrainian forces had seized control of a television tower in Kramatorsk, near the rebel stronghold of Slovyansk where at least three were killed in fighting on Friday, Reuters reported.
"We are not stopping," Avakov said Saturday.
Mourners came out in Odessa, a port city on the Black Sea, a day after at least 42 people died in street fighting and the burning of a building where government opponents took refuge after protesters on both sides threw firebombs at each other. At least 36 people died in the fire, according to the emergencies ministry.
The city's police chief, Petr Lutsyuk, issued a statement calling for calm in the city of about 1 million, and hours later he was fired by Avakov.
Russian President Vladimir Putin's spokesman said the Odessa deaths were evidence that the government in Kiev, which came to power following the toppling of the pro-Russia president after months of protests, encourages nationalist extremists.
"Their arms are up to their elbows in blood," Russian news agencies quoted Dmitry Peskov as saying.
Odessa, southwest of Slovyansk, had not previously seen significant confrontations in Ukraine's crisis. It is the major city between the Crimean peninsula, which Russia annexed in March, and the Moldovan separatist region of Trans-Dniester where Russia has a military peacekeeping contingent.
Kiev has said that Russia ultimately aims to take control of a huge swath of Ukraine from Transdniester to the east.