Several thousand Ukrainian riot police gathered in the early hours of Wednesday morning around Independence Square in central Kiev, where protesters have been demonstrating against the government's decision to pull out of negotiations on a trade pact with the European Union.

Police amassed on all sides of the square housing the protest camp which has been the centre of protests that have gripped Kiev for the past two weeks, just a few hours after the EU's top foreign policy representative Lady Ashton had met Ukraine's president Viktor Yanukovych. Ashton had also been due to meet three opposition leaders who have been leading the protests, including the heavyweight boxer Vitali Klitschko.

On the north side of the square, several hundred riot police rushed a barricade that has been in place for 10 days.

A Ukrainian priest speaks to riot police in Kiev. Photograph: Alexander Zemlianichenko/AP

A priest brandishing a cross walked towards the lines of police but was pushed back as protest leaders announced from the main stage that it was a peaceful protest and called on police to stop their assault. As the mobilisation continued, a religious service was held on the stage with hundreds of protesters chanting. "Tomorrow there will be a million of us."

Witnesses told Reuters that a singer on a stage in the centre of Independence Square urged police not to carry out their orders and not to harm the protesters.

Some protesters held their mobile phones in the air like candles and sang the national anthem.

Earlier, Yanukovych had promised to restart work on an association and free-trade agreement with the European Union, as he sought to quell the protests. He said a delegation would travel to Brussels on Wednesday and suggested the pact he pulled out of last month could be signed in the spring if Ukraine was given better financial conditions.

Riot policemen at Independence Square in Kiev. Photograph: Alexander Zemlianichenko/AP

Yanukovych pulled out of the deal amid pressure from Russia, which wants Ukraine to join its rival Customs Union. Russia is believed to have offered its cash-strapped neighbour financial support and reduced gas prices. "We want to achieve conditions that satisfy Ukraine, Ukrainian producers, the Ukrainian people," said Yanukovych on Tuesday during a televised roundtable discussion with his three predecessors.

Moscow and Brussels have accused each other of putting unacceptable pressure on Kiev. Russia's parliament issued a statement on Tuesday criticising western politicians for openly supporting the protesters in Kiev.

Ashton visited Independence Square, which has been turned into a protest encampment with log fires, food stalls and a stage blaring pop music and speeches from opposition leaders.

Arseniy Yatsenyuk, a member of jailed former prime minister Yulia Tymoshenko's Fatherland party, led Ashton away amid a media scrum and through a police line to waiting cars in which they left for a meeting.

"The most important thing is that all the European leaders to come here have supported not the opposition or political parties but the people on the square," he said.

During the roundtable talk, Ukraine's first president, Leonid Kravchuk, criticised the actions of riot police. "When people are causing disorder, riot police officers should arrest them and take them away, but never beat them. Or even worse, do it in front of cameras," he said.

Yanukovych interrupted him and said: "When they started to attack the riot police, they got their response." He did, however, say that some of those arrested in the clashes should be released.

Kiev's biggest protest since the 2004 Orange Revolution took place on Sunday when hundreds of thousands of people flooded the streets and a small group tore down a statue of Lenin and hacked it to pieces with hammers.