KIEV (AFP) - Ukraine's opposition on Sunday appealed for the first time for international aid and mediation to end a deadly two-month standoff with President Viktor Yanukovych during a rally with over 60,000 protesters.

With still no end in sight for the crisis, the president's office said the 63-year-old Yanukovych was due to return to work on Monday following four days of sick leave with an "acute respiratory infection".

With the opposition so far receiving only verbal pledges of international support, former economy minister Arseniy Yatsenyuk told the crowd: "We spoke to our Western partners and told them that we need real financial aid."

Boxer-turned-politician Vitali Klitschko said there was also a need for an international role to avoid "misunderstandings" in negotiations between the opposition and Yanukovych that have proved inconclusive.

The violence in Ukraine has eased but tensions were still high, as shown by a standoff between opposition lawmakers and police outside a clinic treating an injured protester accused of helping organise riots.

A Kiev court later on Sunday authorised Dmytro Bulatov, whose case has caused international outrage, to leave Ukraine for treatment after he said he was kidnapped and tortured for eight days by unidentified captors.

German Foreign Minister Frank-Walter Steinmeier earlier offered to host Bulatov following talks with his Ukrainian counterpart Leonid Kozhara, who dismissed the man's apparently severe injuries as "a scratch".

Two Russian pro-opposition journalists also said they were stopped by a car with blacked-out windows and no number plate, beaten and told to return to Russia.

At the sprawling protest camp in Kiev that has been the epicentre for demonstrations that have spread across Ukraine, the crowd shouted its defiance against his rule.

Yanukovych has accepted the resignation of his prime minister and repealed hugely controversial anti-protest laws that had radicalised the protest movement.

But the opposition still has a number of demands, including an overhaul of the constitution to take away presidential powers and the unconditional release of all the scores of protesters arrested so far.

The protest movement is also asking for a presidential election scheduled in 2015 to be brought forward to this year, while most of the demonstrators in the streets want Yanukovych to resign immediately.

The army has called for "urgent measures" to deal with the situation and the opposition has warned this could be a prelude to a decree of emergency rule.

But experts say a military intervention is unlikely since the loyalty of hard-up rank and file soldiers faced with protesters could be in doubt.

The 63-year-old leader "should resign along with parliament if he wants a peaceful resolution," said Oksana Hodakivska, a dentist from the northwestern region of Zhytomyr, at the Kiev protest.

Hodakivska said she did not hold out much hope for Western pressure on Yanukovych.

"EU officials can temporarily stop the violence when they visit Ukraine but they are not going to keep coming here.

"It's all in our hands," she said.

But Yuriy Krenyuk, a pensioner from the Ivano-Frankivsk region, said Western powers could help resolve the crisis by putting pressure on the foreign assets held by Ukrainian oligarchs who back Yanukovych.

"If the oligarchs' bank accounts are blocked then the question of Yanukovych's resignation can be resolved very quickly," he said.

"Without the president's resignation, people will not leave the Maidan," he said referring to Independence Square by its local name.

At the rally, former interior minister Yuriy Lutsenko railed against what he termed "a new attempt at colonisation" by Russia.

Ukraine's worst protests since independence in 1991 began when Yanukovych in November turned down a partnership pact with the European Union under pressure from former master Moscow.

Ukraine is struggling to break free of a painful recession and Russia has put on hold until a new government is formed a US$15-billion (S$19.15 billion) bailout package that has been propping up the economy.

What started out as a pro-EU movement has turned into a campaign to oust Yanukovych.

Four people - two protesters and two police officers - have been killed in clashes.

Europe and the United States have pledged to stand behind Ukraine's protest demands and have threatened sanctions against Ukrainian officials.

US Assistant Secretary of State Victoria Nuland is due in Kiev this week, as is the European Union's foreign policy chief Catherine Ashton.

Russia has condemned this as intolerable foreign interference and has dismissed the protesters as far-right extremists bent on violence.