- Armed pro-Moscow activists have seized state buildings in eastern cities
- In Donetsk - the regional capital - protestors occupied the police headquarters forcing the police chief to quit his post and leave the building
- The red, white and blue Russian flag raised in place of the Ukrainian flag
- Occupations have deepened tensions prompting fears of flashpoints
- If any pro-Russian protestors are killed or injured by Ukrainian forces, it could prompt the Kremlin to step in to protect Russian-speaking people
- NATO says Russia is massing troops on Ukraine's eastern border
- Gas crisis could affect millions as Russia threatens to turn off natural gas pumped to the west via Ukraine in row over unpaid bill and rising prices
Armed pro-Russian militants have today raised their flags over official buildings in two eastern Ukrainian cities deepening a stand-off with Moscow, which Kiev warned, could drag Europe closer to the brink of a 'gas war'.
The occupations have deepened tensions in the region, causing potential flashpoints.
If any of the pro-Russian protestors are killed or injured by Ukrainian forces, it could prompt the Kremlin to intervene to protect the local Russian-speaking population in scenes reminiscent of the takeover of Crimea.
Moscow denies any plan to send in forces or split Ukraine, but the Western-leaning authorities in Kiev believe Russia is trying to create a pretext to interfere again.
NATO says Russian armed forces are massing on Ukraine's eastern border, while Moscow says they are on normal manoeuvres.
Ukraine's acting foreign minister, Andrii Deshchytsia, said he had spoken in a phone call with Russian Foreign Minister Sergei Lavrov and demanded Moscow stop what he called 'provocative actions' by its agents in eastern Ukraine.
Russia and Ukraine have been in confrontation since protests in Kiev forced the Moscow-backed president from office, and the Kremlin sent troops into Crimea.
The crisis has been seized upon by some right-wing nationalists in the EU who are campaigning for next month's European Parliament elections. They blame Brussels for antagonising Russia.
Marine Le Pen, leader of France's far-right National Front was in Moscow on Saturday and met the speaker of Russia's lower house of parliament, one of the people on an EU sanctions list.
'I am surprised a Cold War on Russia has been declared in the European Union,' Russian media quoted her as saying.
US Vice President Joe Biden will travel to Ukraine later this month, officials said Saturday, as Washington warned Moscow of “additional consequences” if it fails to reduce tensions with Ukraine.
The announcement came just a day after Washington unveiled sanctions against six of Crimea’s breakaway leaders, including the official who signed the deal with Moscow to split the peninsula from Ukraine.
Fears of further Russian land-grabs in Ukraine grew on Saturday as pro-Kremlin gunmen mounted a series of co-ordinated assaults on police stations and security buildings.
The operations came as Sergei Lavrov, Russia’s foreign minister, said Ukraine was “demonstrating its inability to take responsibility for the fate of the country”.
In what many fear could be the prelude to a full invasion by Russian troops, masked men armed with Kalashnikovs and stun grenades seized two police stations and an intelligence headquarters in eastern Ukraine.
Believed to include professional soldiers in their ranks, the gunmen also set up checkpoints along local roads and began barricading the buildings. There were reports of gunfire, but no casualties.
The operations followed a period of relative calm in eastern Ukraine, where the pro-Russian movement that had occupied a number of town hall buildings appeared to have lost momentum.
But the Ukrainian government, which on Saturday evening convened an emergency security meeting, has long maintained that the Kremlin was simply biding its time.
The White House echoed the fears of observers on the ground who said the attacks bore a speed and professionalism reminiscent of the early stages of Russia’s Crimea annexation. It warned Russia against further military action.
“We saw similar so-called protest activities in Crimea before Russia’s purported annexation,” said Laura Lucas Magnuson, a spokesman for the White House National Security Council.
Vladimir Putin, the country’s president, should “cease all efforts to destabilise Ukraine”, she added.
The gunmen's main focus of attack was Slavyansk, a city of 120,000 people that lies on a river 35 miles from Donetsk, Ukraine's eastern regional capital.
After raising the Russian flag at both the police station and the local security service headquarters, they ransacked the police station armoury of at least 400 handguns and 20 automatic weapons.
"The aim of the takeover was the guns," a Ukrainian police statement said. "They are giving these guns to participants in the protest in Slavyansk."
The men standing guard behind newly erected barricades appeared to include professional soldiers as well as retired veterans and civilian volunteers. Some said they wanted a referendum on becoming part of Russia, as Crimea did last month.
"For three months we have been demanding a referendum and they haven't listened to us," one armed man told The Sunday Telegraph,describing himself as a veteran of Afghanistan.
"Since that war I have not picked up a gun, I became a builder and tried to forget a war. After this, I'll put it away and never need it again," he said, tapping a loaded AK-47.
Asked where the weapons came from, he nodded at the Russian flag now flying from the police station and said: "Look at that flag. You know which country that represents."
Meanwhile, in Donetsk, around 200 pro-Russian protesters armed with clubs and sticks stormed the regional police headquarters without resistance from anyone inside. Witnesses said they wore the uniforms of the Berkut, the feared riot police squad accused of taking part in shootings that killed over 100 people during the anti-government protests that toppled President Viktor Yanukovych.
Pro-Russian activists stand in front of a barricade outside the regional state administration building in Donetsk (Max Vetrov/ Getty)
Later, anti-riot police who arrived at the scene were seen sporting orange and black ribbons, symbolising support for Russian rule
The local police chief also went on national television and said he was resigning.
Arsen Avakov, Ukraine's interior minister, pledged to deal with the unrest, saying: "The response will be very tough because there is a difference between protesters and terrorists".
But it is likely to be a strong test of nerve for the Ukrainian security forces, who know that any serious bloodshed could give Russia a pretext to intervene to "protect" pro-Russian elements.