Ukraine's new acting government is not legitimate, Russian prime minister Dmitr y Medvedev has said. "If people crossing Kiev in black masks and Kalashnikov rifles are considered a governmen t, it will be difficult for us to work with such a government," the prime minister said. "Some of our foreign, western partners think otherwise, considering them to be legitimate authorities. I do not know which constitution, which laws, they were reading, but it seems to me it is an aberration of perception when somethin g that is essentially the result of a mutiny is called legitimate." He also called the legitimacy of many of Ukraine's governing bodies "doubtful", adding: "There is no one to deal with there [in Ukraine]; masked and armed people are no partners for dialogue." The Russian PM said he did not understand what was happening in Ukraine. "There is a real threat to our interests and to the lives of our citizens," he said. "There are big doubts about the legitimacy of a whole series of organs of power that are now functioning there." But Medvedev also said any legally-binding Russian-Ukranian agreements "must be honoured". There are fears about the future of a gas deal agreed in December under which Russia reduced the gas price for Kiev to $268.50 per 1,000 cubic metres, from the $400 which Ukraine had paid since 2009. "Those agreements which are legally binding must be honoured," Medvedev said. "We are not cooperating with personalities or isolated individuals. These are inter-state relations. We are neighbours, close nations, and we cannot run away from one another. Whatever has been signed must be honoured. For us, Ukraine remains a serious and important partner." Vladimir Putin, Russia's president, has yet to comment on the events that swept Ukrainian president Viktor Yanukovych out of power on Saturday. The hunt is now on for Yanukovych, who is currently believed to be hiding in the pro- Russian Crimean peninsula. The country's new acting government has issued a warrant for his arrest, accusing him of the mass murder of protesters who died in street clashes last week. Ukraine's acting interior minister, Arsen Avakhov, said on his official Facebook page on Monday that a warrant had been issued for the arrest of Yanukovych and several other officials for the "mass killing of civilians". At least 82 people, primarily protesters, were killed in clashes in the capital, Kiev, last week. After signing an agreement with the oppo sition, Yanu kovych fled the capital for eastern Ukraine. Avakhov said he tried to fl y out of Donetsk but was stopped, then went to Crimea. Yanukovych appeared in a video address on Saturday evening claiming he was still the president, but he has lost the support of most of his party and his main goal now will probably be to flee the country without being arrested. Avakhov said Y anukovych ar rived in Crimea on Sund ay, relinquish ed his official se curity detail and then drove off to an unknown location. There were rumours that a yacht named the Bandido, believed to belong to Yanukovych's son, was spotted in the harbour in the Crimean port of Balaclava. In Balaclava on Monday there was no sign of either the yacht or the president, and locals claimed they had not seen Yanukovych in recent days. Officials in Sevastopol also professed ignoran ce. In Kiev, western diplomats said they had no idea of the president's location. Calls are mounting in Ukraine to put Yanukovych on trial after a tumultuous presidency in which he amassed powers, enriched his allies and cracked down on demonstrators. Anger boiled over last week after snipers attacked protesters in the bloodiest violence in Ukraine's post-Soviet history.