Russian President Vladimir Putin has weighed in his neighbour's future on live television.
In a four-hour televised question-and-answer session, Putin dismissed as "nonsense" claims that Russian special forces were fomenting the unrest in eastern Ukraine.
"It's all nonsense, there are no Russian units, special forces or instructors in the east of Ukraine," Putin said.
He did admit, for the first time, that the troops in unmarked uniforms who had captured Ukraine's Crimean Peninsula before its annexation last month by Moscow were Russian soldiers.
Putin also expressed hope that four-way talks between Ukraine, the US, the European Union and Russia in Geneva on Thursday could map a way out of one of Europe's greatest security threats in decades.
Protesters gathered on Thursday in front of the occupied city hall which is flying a flag in Russian colours and proclaiming an independent eastern state.
Hundreds of demonstrators staged the rally in the eastern city of Mariupol after Ukrainian soldiers killed three people during a raid on their barracks.
The three assailants were killed and 13 others wounded when around 300 people attacked the interior ministry troops in the industrial port city overnight with firearms and petrol bombs, according to Interior Minister Arsen Avakov.
After warning shots, the troops fired on the assailants, resulting in the deaths, he said, adding that 63 people were arrested and "Russian cell phones" were seized.
The interior ministry said additional police had been sent to Mariupol and special forces were helicoptered in as reinforcements.
The attack followed the seizure of administrative buildings by pro-Russian separatists in Mariupol and other towns across the restive east of the country.
There were no casualties among Ukrainian servicemen, the ministry said. At least 63 people involved in the attack were detained, but local media cited police as saying 38 were later released.
The southern Ukrainian city lies on the road running from Russia along the coast to Crimea, the peninsula that Russia annexed last month. NATO says Russia has up to 40,000 troops along its border with Ukraine.
Also on Thursday, Ukraine's prime minister accused Russian President Vladimir Putin of trying to sabotage the country's upcoming presidential election and said Moscow was responsible for deaths in recent clashes in eastern Ukraine.
"Russia is playing only one game: further aggravation, further provocation, because the task, that Putin today officially announced, is to wreck the presidential election on May 25," Arseny Yatseniuk told reporters.