(Adds new violence in square, EU foreign ministers in Kiev)
* Protesters force riot police from Kiev square, capture policemen
* Truce shaky after death of 28 people in violence on Tuesday
* U.S. imposes visa bans on 20 senior Ukrainian officials
* Polish, French, German foreign ministers in Kiev for talks
By Richard Balmforth and Pavel Polityuk
Feb 20 (Reuters) - Ukrainian protesters hurling petrol bombs and paving stones drove riot police from the central square in Kiev on Thursday despite a "truce" which embattled Ukrainian President Viktor Yanukovich said he had agreed with opposition leaders.
Afterward, a Reuters photographer saw 10 dead in civilian clothing in two places on Independence Square, known as Maidan, where pro-European demonstrators have been encamped for three months. Television also showed activists in combat fatigues leading away several uniformed policemen they had captured.
The crowd had surged forward to recapture a corner of the square, closest to the presidency and parliament, which riot police had occupied late on Tuesday. Since then, 28 people, including 10 policemen, have been killed in the worst violence since Ukraine became independent of the Soviet Union in 1991.
Both sides have accused the other of using live ammunition.
The flare-up, just as three European foreign ministers arrived in Kiev for talks with Yanukovich to try to promote a political compromise, broke a tense stand-off in the city centre, now alive with wailing police and ambulance sirens.
Parliament was evacuated, local media said, and it was unclear how the violence would affect the plans of the EU delegation of ministers from Germany, France and Poland.
The crisis in the sprawling country of 46 million with an ailing economy and endemic corruption has mounted since Yanukovich pulled out of a planned far-reaching trade agreement with the EU in November under fierce pressure from Moscow and agreed to take a $15-billion Russian bailout instead.
The United States stepped up pressure on Wednesday by imposing travel bans on 20 senior Ukrainian officials, and European Union foreign ministers are due to meet in Brussels later on Thursday to consider similar measures.
A statement on Yanukovich's website announced an accord late on Wednesday with opposition leaders for "the start to negotiations with the aim of ending bloodshed, and stabilising the situation in the state in the interest of social peace".
Responding cautiously, U.S. President Barack Obama deemed the truce a "welcome step forward", but said the White House would continue to monitor the situation closely to "ensure that actions mirror words".
"Our approach in the United States is not to see these as some Cold War chessboard in which we're in competition with Russia," Obama said after a North American summit in Mexico.
"Our goal is to make sure that the people of Ukraine are able to make decisions for themselves for the future, that the people of Syria are able to make decisions without having bombs going off and killing women and children," he said.
Protesters were in a truculent mood despite the overnight lull and columns of men, bearing clubs and chanting patriotic songs headed to Independence Square at 8:30 a.m. (0630 GMT).
"What truce? There is no truce! It is simply war ahead of us! They are provoking us. They throw grenades at us. Burn our homes. We have been here for three months and during that time nothing burned," said 23-year-old Petro Maksimchuk.
"These are not people. They are killers. Sanctions will not help. They all should be sent into isolation in Siberia."
Serhiy, a 55-year-old from the western city of Lviv who declined to give his surname, added: "It is bad that Ukraine is already broken into two parts. In the west the police and army are with us but in the east, they are against us.
"It is the 'Yanukovichers' who are dividing us."
In Lviv, a bastion of Ukrainian nationalism since Soviet times, the regional assembly declared autonomy from Yanukovich and his administration, which many west Ukrainians see as much closer to Moscow and to Ukraine's Russian-speaking east.
The health ministry revised upwards the death toll in Tuesday's violence to 28 as of 6 a.m. on Thursday - three hours before the latest violence.
Yanukovich, who replaced the head of the armed forces, had denounced the bloodshed in central Kiev as an attempted coup. His security service said launched a nationwide "anti-terrorist operation" after arms and ammunition dumps were looted.
Reflecting Western outrage at the crackdown, EU ambassadors discussed a series of possible steps including asset freezes and travel, even though many diplomats have doubts about the effectiveness of such sanctions.
"The European Union will respond to the deterioration on the ground, including via targeted measures," European Council President Herman Van Rompuy said in a statement, while holding out the possibility of trade and political agreement with Ukraine if it meets goals agreed on with the EU.
Jumping out ahead of its EU allies, Washington imposed U.S. visa bans on 20 Ukrainian government officials it considered "responsible for ordering human rights abuses related to political oppression", a senior State Department official said.
"These individuals represent the full chain of command we consider responsible for ordering the security forces to move against" the protesters, the official said.
While declining to name those affected by the bans, which bar them from applying for visas to travel to the United States, the U.S. official said the restrictions were easily reversible if the situation improved.
EU officials said Yanukovich himself would be excluded from such measures in order to keep channels of dialogue open.
As well as asset freezes and visa bans, ministers will discuss measures to stop riot gear and other equipment being exported to Ukraine and could consider arms restrictions.
Diplomats said the threat of sanctions could also target assets held in the West by Ukrainian business magnates known as the oligarchs who have either backed Yanukovich or are sitting on the fence.
The United States, going head to head with Russia in a dispute reminiscent of the Cold War, urged Yanukovich to pull back riot police, call a truce and talk to the opposition.
Obama warned the Ukrainian armed forces that the crackdown could damage "our defence relationship". But Washington appears to have little direct leverage in Kiev.
Russian President Vladimir Putin, who has met Yanukovich six times since the crisis began, has kept quiet in public on the latest flare-up. But Foreign Minister Sergei Lavrov blamed the West for encouraging opposition radicals "to act outside of the law."
Moscow announced on Monday it would resume stalled aid to Kiev, pledging $2 billion just hours before the crackdown began. The money has not yet arrived, and a Ukrainian government source said it had been delayed until Friday "for technical reasons."
Putin's spokesman said on Thursday, however, that Moscow was waiting for the situation to normalise before paying up.
Ukraine's hryvnia currency, flirting with its lowest levels since the global financial crisis five years ago, weakened to more than 9 per dollar for the second time this month.
Possibly due to the risk of sanctions, three of Ukraine's richest entrepreneurs have stepped up pressure on Yanukovich to hold back from using force and make every effort to solve the crisis through negotiation with the opposition.
"There are no circumstances which justify the use of force toward the peaceful population," steel and coal magnate Rinat Akhmetov said in a statement late on Tuesday.
Akhmetov, who partly bankrolled Yanukovich's election campaign in 2010 and whose wealth is put by Forbes at more than $15 billion, said: "People's deaths and injuries on the side of protesters and the security forces in street battles are an unacceptable price for political mistakes."
Viktor Pinchuk, another steel billionaire known in the West for his philanthropic activity, said: "A peaceful solution must be found. It is imperative to refrain from the use of force and find a compromise. ... It is time for all sides to take courageous steps toward compromise."
Dmytro Firtash, a gas and chemicals magnate who is part owner of popular TV channel Inter, said in a statement: We, through our joint actions, must end the bloodshed. We are against radical actions by whomever it might be." (Additional reporting by Natalya Zinets and Alessandra Prentice; Writing By Richard Balmforth and Paul Taylor; Editing by Alastair MacDonald)
Our Standards: The Thomson Reuters Trust Principles.