Pro-Russian­ militants, boasting that they do not take orders from diplomats in Washington or Moscow, refused to end their armed occupation of a dozen government buildings across eastern Ukraine on Friday, upending hopes for a quick end to the standoff.

The conflict between pro-Russian gunmen and Ukrainian authorities turned bloody on Sunday, with one security serviceman killed and reports of people wounded on both sides.

The conflict between pro-Russian gunmen and Ukrainian authorities turned bloody on Sunday, with one security serviceman killed and reports of people wounded on both sides.

KIEV — The Ukrainian government in Kiev on Tuesday announced the start of a staged counter offensive to reclaim control of the country's east as Russian prime minister Dmitry Medvedev warned that Ukraine was descending into civil war.

Facing mounting pressure to act as official buildings in at least nine cities in the restive east have slipped into the hands of pro-Russian separatists, acting Ukrainian President Oleksandr Turchynov said that a counter-terrorism operation had begun in the northern Donetsk region early Tuesday. But there were no immediate signs of a major military offensive, and the government in Kiev remained in a tight spot.

There is deep uncertainty over the technical ability of Ukraine's underfunded and demoralized military to respond to pro-Russian forces, some of whom are heavily armed. At the same time, the government in Kiev was balancing calls for action against the possibility that too strong of a response could prompt Russian troops stationed just across the border to more directly intervene.

“A counter-terrorism operation was launched in the north of Donetsk region,” Turchynov told parliament on Tuesday. “But it will go on gradually, responsibly and prudently. Once again I emphasize that these actions are meant for the protection of Ukrainian citizens, stopping terror, criminality and attempts to break our country into pieces.”

In Donetsk, Mayor Alexander Lukyanchenko pleaded with pro-Russian activists not to make good on a threat to storm the city council offices on Tuesday. “If the city authorities are paralyzed, it would be the detriment of all inhabitants of the city,” he told a press conference on Tuesday.

Underscoring the pressure from Russia, Medvedev on Tuesday slammed the interim government in Kiev for falling into a trap of its own making.

“ The country is on the brink of a civil war. It’s very sad,” Medvedev said on his Facebook page,. He laid blame for the unrest at Kiev’s door saying the new authorities who had seized power “illegally” in a revolution in February had unleashed a wave of violence that they were now unable to control.

“The illegal rulers are trying to restore the order they cynically trampled on when they participated in an armed uprising,” he wrote. “They are falling into their own trap.”

Defiant pro-Russian militants in eastern Ukraine pushed the country to the brink of war or dissolution Monday, expanding their hold while the acting president failed to make headway in trying to end the crisis.

In a nation of 44 million, it became clear that a few hundred men, operating on the eastern fringes of the country with guns and unmarked uniforms, have brought Ukraine to a deeply dangerous juncture.

After an ultimatum to the militants was ignored, Turchynov first vowed to rout them by force, then held out the offer of a referendum to decide Ukraine’s fate, then proposed a peacekeeping intervention by the United Nations.

Nothing Turchynov said moved the pro-Russian forces, who seized another police station in another small town, Horlivka.

Medvedev said he was sorry for the people of Ukraine who had become “hostages of untalented politicians whom they did not elect and irresponsible radicals who had replaced the police and army.”

Claiming that “every cloud has a silver lining,” Medvedev said that many Ukrainians had lost faith in the interim government and realized that the only way to create a “fair society” was with a legal mandate where people were able to decide their own future.

That goal should be achieved “without imposters, nationalists or bandits and without tanks, APC;s or secret visits by the director of the CIA,” he said.

Russia’s foreign ministry warned Ukraine against launching an offensive in south eastern Ukraine saying the action would derail four party international talks in Geneva aimed at resolving the crisis.

Officials from the US, the European Union, Russia and Ukraine are expected to meet in Geneva on Thursday to seek a diplomatic resolution of the crisis in Ukraine where protests have recently intensified in south eastern regions bordering Russia.

“If force is used in southeastern Ukraine, the chances of holding the Geneva meeting would be undermined,” Sergei Lavrov, Russian foreign minister, told a press conference in Beijing on Tuesday.

The mood was tense in Donetsk, a city of nearly 1 million, where many residents were staying inside after dark. Pro-Russian activists took over the regional administrative offices last week, and bands of masked men, including several carrying steel pipes, were patrolling the barricaded entrances to the monolithic structure in the center of town.

Turchynov and other Ukrainian officials are sure that Russia is guiding the militants as they have steadily taken over one government building after another. They have vocal support on that score from Washington and London. Russia adamantly denies it, and the Russian foreign minister, Sergei Lavrov, said Monday it is the West’s responsibility to rein in the government in Kiev so that there are no violent attacks on the militants.

The crisis, which began to the south, in Crimea, is now focused on militants who say they represent the “People’s Republic of Donetsk.” It has brought relations between Russia and the West to their lowest point at least since the Soviet invasion of Afghanistan in 1979.

"There can't really be any real doubt that this is something that has been planned and brought about by Russia," the British foreign secretary, William Hague, said as he arrived in Luxembourg to meet with his European counterparts.

A spokesman for Vladimir Putin said the Russian president has been watching the crisis with “great concern’’ and had received “many appeals, addressed personally to Putin, asking to help in this or that way and asking to intervene in this or that way.’’

Officials at the Pentagon on Monday protested what they described as a provocative flyover by a Russian attack aircraft that flew at close range for 90 minutes over a U.S. Navy ship that had been sent into the Black Sea.

The anonymous appeal for help has been a favorite tactic of Russian interventionists for the better part of a century. It was rolled out before the invasion of Hungary in 1956 and of Czechoslovakia in 1968, two operations in which one of Putin’s heroes, Yuri Andropov, a KGB official who later became Soviet leader, played a key role.

It was also a feature of Russia’s involvement in Crimea in late February and March before that region’s annexation by Moscow.

In eastern Ukraine, Ukrainian news agencies reported Monday evening that opponents of the separatists had set up checkpoints on highways leading from the Donetsk region to the Kharkiv region, and — with the help of traffic police — were inspecting cars with the aim of preventing separatists from traveling to Kharkiv.

But as the evening wore on there was still no sign of Turchynov’s promised attack on separatist positions by forces loyal to Kiev. Turchynov and other officials had said that if no resolution was reached by 8 a.m. Monday, an “anti-terrorist” operation would begin.

In the heart of Donetsk, a group of pro-Russians occupying the city's Lenin Square said they were convinced that the Kiev government would not carry out its threat to deploy the Ukrainian army in the region. Unlike some activists, they said they did not want the Russian military to roll into the region. They were holding out for a referendum on the region's future.

"We are not afraid," said Oles Kulik, a retired coal miner occupying a tent in the square and where banners declaring the People’s Republic were plastered on lampposts. “Kiev needs to hear our voice and understand that we are now something different from them.”

Elsewhere in the region, the several hundred pro-Russian militants have established themselves in towns on strategic crossroads, but wouldn’t be able to withstand an armored assault — unless such an attack draws assistance from Russian military forces right across the border, which is exactly what Kiev and its friends abroad fear.

This being Ukraine, though, some people — including Oleksandr Yaroshenko, a veteran political strategist in Donetsk — worry that Turchynov and his ally, the former prime minister Yulia Tymoshenko, are gaming the crisis for personal benefit and may not intend to resist Russia to the fullest.

One factor at play is the upcoming presidential election, scheduled for May 25 but looking increasingly unlikely. On Monday, Turchynov unexpectedly held out the offer of a referendum to determine the amount of power-sharing between Kiev and the regions, to be held the same day. The separatists have been saying that a referendum is their principal goal, but many were quick to dismiss Turchynov’s proposal as insincere — as was the Russian foreign ministry.

Turchynov also talked with U.N. General Secretary Ban Ki-moon and later suggested that a U.N. peacekeeping force could enter eastern Ukraine. But the almost-certain opposition of Moscow, standing up for the men with guns, makes that problematic.

Those loyal to Kiev in Donetsk appeared to be running out of patience.

“From the government’s actions so far, we are reading that the pro-Ukrainian citizens of Donetsk are being left behind,” said Diana, a 34-year-old graphic designer who would not give her last name out of fear for her safety. “The situation here is critical, and what we need from Kiev is action.”

Secretary of State John F. Kerry and European leaders are promising more sanctions, on top of those imposed on Russia over its role in Crimea. The State Department circulated a document assailing what it called “Russian Fiction: The Sequel. Ten More False Claims about Ukraine.”

In seeking to contradict assertions from Moscow, the American document says, among other things, that Russian agents are active in eastern Ukraine; that separatists there do not enjoy broad popular support; that Russian-speakers are not under threat; and the new government in Kiev is not led by right-wing nationalists and fascists.

“I don’t think denials of Russian involvement have a shred of credibility,” British official Hague said Monday.

Englund reported from Moscow and Karla Adam contributed reporting from London.