KIEV — Ukraine's embattled president announced he would return to work after four days' sick leave, as protesters filled Kiev's main square on Sunday demanding he give up power.
Opposition leaders, addressing the crowd on their return home from meeting European and U.S. officials, said they hoped for international mediation in negotiations with the government and for constitutional change to limit presidential power.
Calling for a complete change of leadership after weeks of crisis that have divided the country and set the West against Yanukovych's Russian allies, opposition figures who attended a security conference in Munich told supporters they would secure international economic aid if they were able to take power.
Yanukovych, who angered opponents in November by spurning a trade pact with the European Union and turning instead to Moscow for financial support, announced on Thursday he was on sick leave and has not been seen in public since.
Critics saw in his absence a tactic to deflect pressure for political compromise. On Friday, he signed legislation revoking unpopular new restrictions on protest meetings that has, however, failed to appease opponents who are demanding the release of dozens of people arrested in recent weeks.
On Sunday, a presidential statement said Yanukovych planned to return to work Monday after an acute respiratory infection: "After undergoing required treatment, the president of Ukraine feels well and his health is satisfactory," said a state medical official, Alexander Orda.
On the capital's Independence Square, the focus of a sprawling, barricaded protest camp throughout the winter, thousands of people gathered to listen to opposition leaders despite a freezing wind and Arctic temperatures which helped keep attendance well below those of major rallies in recent weeks.
Vitali Klitschko, a former world champion heavyweight boxer-turned-politician, said they had discussed with senior Western officials in Munich bringing in international mediators in talks with the Ukrainian authorities.
"The democratic world has understood that there is no trust in the Yanukovych regime," he told the crowd."So we spoke about international mediation in negotiations with Yanukovych, so that afterward there will no differing interpretations of obligations."
Arseny Yatsenyuk of the Fatherland party, who turned down an offer last week from Yanukovych to become prime minister, called on the authorities to free 116 prisoners. The president signed a law allowing protesters to be set free — but only once demonstrators stop occupying public buildings.
Yatsenyuk also renewed a call for a release of his party's leader, former Prime Minister Yulia Tymoshenko, whose freedom has also been a demand of the EU. He added that there should be an international inquiry into "the criminal regime," held under the auspices of the Council of Europe.
"We told our Western partners we need real financial help to get the country out of crisis," Yatsenyuk said.
"But when we say 'we', we mean the Ukrainian people — not a penny must go to the Yanukovych regime.
"They are ready to help the Ukrainian people. But we must restore popular authority," he added. "Parliament must amend the constitution and get rid of the dictatorial powers of the president."
Some opposition leaders have urged the EU, whose foreign policy chief Catherine Ashton is due in Kiev on Tuesday, to impose sanctions to hurt the business and financial interests of the president and his leading supporters. However, few European governments see that as worthwhile at present.
Ashton said in Munich on Sunday: "It is really important first and foremost that the violence in Ukraine stops, and that they move to a constructive dialogue, look at the issues of constitutional reform, the role of parliament and moving forward so that people can have faith in the transparency and openness of the process that will eventually of course lead them to free and fair elections in the future."
A senior U.S. State Department official is also due to visit Kiev this week.
At least six people were killed during protests last month and some leading figures have warned of "civil war." Since the resignation a week ago of Yanukovych's prime minister, the government has been operating in an interim capacity and some opposition leaders say they fear the president might impose a state of emergency or military rule on the country.
"Ukraine desperately needs a Marshall Plan and not martial law," Yatsenyuk said in Munich on Saturday, referring to the massive U.S. aid to western Europe after World War II.
Foreign Minister Sergei Lavrov, also in Munich, criticized the West for trying to force Ukraine into forging closer ties.