Three months of confrontation in Ukraine between the president and a large protest movement reached its peak on Tuesday night in the worst bloodshed since the country separated from Moscow more than two decades ago, with 18 people reported killed as riot police moved in to clear Kiev's Independence Square, the crucible of the anti-government activism, the Guardian reported.
Hopes for a settlement of the crisis went up in smoke amid scenes of rioting, burning buildings, police bombings and rubber bullets that also left up to 500 people injured.
A large section of the protest camp in the capital, Kiev, was engulfed in flames on Tuesday night as police advanced on the demonstrators using water cannons and stun grenades.
The security services had earlier issued a warning, ordering tens of thousands of protesters to get off the streets by Tuesday evening or face a crackdown.
The violence, the worst since a government-opposition confrontation erupted last November, came after President Viktor Yanukovych, the main target of the protests, stalled on outlines of an agreement to appoint a new technocratic coalition government or have his powers cut back.
Opposition organisers said 11 civilians had been killed and hundreds more injured, many seriously. The authorities said seven police officers were killed and 39 officers had sustained gunshot wounds.
Columns of riot police sought to banish crowds of protesters from encroaching on the country's parliament, while demonstrators ransacked offices of Yanukovych's political party.
"Extremists are killing innocents on the streets of the capital, burning buildings and cars," the statement from the security services said. "Unless the disorder stops, we will have to restore order by all means envisaged by law."
The White House asked Yanukovych to "exercise maximum restraint". But video footage from Kiev showed heavily armed riot police firing Kalashnikovs. Both police and opposition leaders called on women and children to leave the protest camp in Independence Square, known as the Maidan, as riot police began their assault.
Vitali Klitschko, an opposition leader and former world heavyweight boxing champion, said: "The government has deliberately organised a provocation to clear Independence Square with blood and violence and to destroy the protests and the activists."
There were reports that riot police were firing smoke and stun grenades. Opposition sources said police snipers were firing on demonstrators from rooftops. According to reports, security services began moving in at 8pm local time after announcing over loudspeakers that they were about to conduct "an anti-terror operation".
The foreign ministries of Ukraine and Russia earlier issued what appeared to be co-ordinated statements blaming Europe for fomenting the unrest. It appeared that the Kremlin had a hand in the political machinations behind the eruption and the crackdown. As well as blaming Europe for the rioting, it offered $2bn (£1.2m) to Yanukovych and sought to influence the appointment of the new prime minister.
"The violent clashes today have to date resulted in deaths by bullets and hundreds of injuries, including seven people in a critical position," said protesters in a statement.
"Snipers posted on roofs are targeting the heads and chests of protesters. Ambulances blocked by security forces are not able to provide first aid to the injured," it continued.
Protesters, some of them armed with air pistols and petrol bombs, hurled bricks and paving stones at ranks of riot police, who used rubber bullets, smoke and stun grenades. Many of the injuries were said to have been head wounds from being struck by grenades.
The EU's foreign policy chief, Catherine Ashton, said she was "deeply worried about the grave new escalation". UN secretary general, Ban Ki-moon, called for restraint and dialogue, while Washington said it was appalled by the violence and demanded that Yanukovych must "de-escalate the situation". Nato's secretary-general, Anders Fogh Rasmussen, urged "all parties to refrain from violence and to urgently resume dialogue, including through the parliamentary process".
While chaos and bloodshed reigned on the streets of central Kiev, there were also scenes of mayhem inside parliament, where opposition leaders sought to inaugurate moves curbing the powers of the president and making Ukraine more of a parliamentary than a presidential system.
The opposition tried to table a resolution returning the country to its 2004 constitution, which would have given parliament the authority to appoint a new prime minister and cabinet and strip Yanukovych of many of his powers.
The president's allies in parliament simply blocked the move, refusing to have the resolution registered. Yanukovych orchestrated changes to the 2004 constitution after taking power in 2010 and vesting most powers in his own office.
Earlier, several thousand nationalists led by the Svoboda [freedom] party converged on a park near the parliament and tried to move on the legislature, only to be blocked by riot police who also closed down the city centre metro system.
The flare-up and apparent readiness for a draconian crackdown followed several days of signs that the crisis was ebbing and compromises were being reached.
Protesters evacuated several buildings they had been occupying for months, including Kiev city hall, which was set ablaze.
In recent days authorities have released more than 240 people detained during the unrest under an amnesty.
Yanukovych is to meet a trio of opposition leaders on Wednesday and is expected to propose a new prime minister.
Last November confrontation was sparked when Yanukovych abruptly ditched years of negotiations with the EU on a political and free trade pact, turning instead to Moscow for $15bn-worth of cheap loans and discounted gas supplies.
Moscow promptly responded by buying $3bn-worth of Ukrainian bonds, but then stopped lending last month when Yanukovych sacrificed his pro-Kremlin prime minister, Mykola Azarov.
The offer on Tuesday of a new $2bn loan was seen as tied to Yanukovych making the "right" choice for new prime minister.
The swiftness of the Russian moves in seeking to outwit the EU in what rapidly snowballed into a contest for influence in Ukraine has exposed the lumbering nature of European diplomacy and policy-making in a crisis in a neighbouring state.
The opposition leaders and protesters are seeking to unseat Yanukovych and force early presidential elections.
Vitali Klitschko told parliament Yanukovych should "call snap presidential and parliamentary elections. Do it. It's the only way to solve the issue.".