Four Ukraine troops killed in gun battles with pro-Russia forces
Four troops have been killed and 30 wounded in gun battles with pro-Russia militants occupying the eastern city of Slovyansk, according to Ukraine's interior ministry.
Slovyansk has been at the heart of an uprising in east Ukraine against the central government in Kiev, which came to power after the country's Russia-leaning president fled following months of street protests.
A statement on the ministry's website did not give further details about how the officers died. But a separate statement said Ukrainian troops had started an "anti-terrorist operation" against the pro-Russia forces, which numbered around 800.
The government has also sent an elite national guard unit to re-establish control over the southern port city of Odessa.
The twin moves reflected an apparent escalation of efforts to bring both regions back under Kiev's control.
Any possible loss of Odessa in the west and parts of eastern Ukraine could leave the sprawling country landlocked, cut off entirely from the Black Sea. Russia has already annexed a significant part of Ukraine's Black Sea coast in grabbing back the peninsula of Crimea.
A pro-Russia militia spokesman in Slovyansk said an unspecified number of people had been killed and wounded in the clashes, including a 20-year-old woman killed by a stray bullet.
Both sides indicated fighting was taking place at several sites around the city.
Earlier, Germany said it is pushing for a second round of diplomatic talks in Geneva in an effort to halt the violence in Ukraine.
Foreign minister Frank-Walter Steinmeier said all parties must push for a return to the accord reached in Switzerland last month encouraging all sides to lay down arms.
Mr Steinmeier said new talks are needed in the wake of recent violence to produce a "clear conclusion as to how this conflict can be brought to a halt".
He said he has been pushing for the meeting with Russian foreign minister Sergey Lavrov, US secretary of state John Kerry, the European Union and the Organisation for Security and Co-operation in Europe (OSCE).
Mr Steinmeier called for an expanded OSCE role, saying its observers had provided "highly important" information.
Yesterday, police in Odessa freed some detained activists after hundreds of pro-Russian demonstrators stormed police headquarters in the Ukrainian port city.
The interior ministry said that 67 people who were detained after deadly clashes were released.
More than 40 people died in the clashes on Friday, some from gunshot wounds, but most in a fire that tore through a trade union building.
Ukrainian prime minister Arseniy Yatsenyuk visited Odessa to try to defuse mounting tensions. He said police are being investigated for their failure to maintain order and hinted strongly that he sees Moscow's hand in the unrest.
Meanwhile, pro-Russian activists in Odessa have vowed to take city buildings after attending the funeral of a politician who died in the fire that killed over 40 people last week.
Regional parliament member Vyacheslav Markin, who was known for speaking out against the government in Kiev, was buried today while about 300 pro-Russian supporters shouted "Hero, hero!". Mr Markin died on Sunday from burn wounds sustained in Friday's fire.
Many of those at the funeral wore the St George black-and-orange ribbon that has become a ubiquitous symbol of the pro-Russian protest movement in Ukraine and said they were planning to storm the regional government building in Odessa later.
Pro-Russian militants have seized administrative buildings and police stations across much of southern and eastern Ukraine.