German Chancellor Angela Merkel expressed outrage on Friday over a leaked phone conversation in which a top U.S. diplomat used the f-word regarding the European Union's handling of the crisis in Ukraine.

The candid remark by the U.S. State Department's most senior European official threatened to drive a dangerous divide between the allies in the midst of one their most high-stakes diplomatic tussles with Moscow since the Cold War.

Ukrainian President Viktor Yanukovych told a senior U.S. envoy Thursday he wanted to quickly adopt constitutional changes called for by the pro-Western opposition, which would see him cede some powers to parliament.

A presidential statement said the Ukrainian leader "backs the quickest possible implementation of constitutional reforms", while also telling U.S. Assistant Secretary of State Victoria Nuland that he favored "dialogue and compromise" with the opposition.

A man had his hand blown off when a package exploded in a building occupied by Ukrainian protesters in Kiev on Thursday, police said.

"He opened some sort of box, after which the blast happened," police said in a statement.

European lawmakers called Thursday for targeted EU sanctions against the Ukraine government and those implicated in violence against pro-EU demonstrators.

A non-binding resolution said the European Union and member states should consider travel bans and asset freezes on "Ukrainian officials, legislators and oligarchs personally responsible for the attacks on and deaths of protesters".

An adviser to Russian President Vladimir Putin accused Washington on Thursday of financing and arming Ukrainian militants as a senior U.S. official arrived for crisis talks in Kiev.

Putin's economic adviser Sergei Glazyev, often seen as the Kremlin's pointman on Ukraine, also suggested that Russia had legal grounds to intervene in the two-month-old crisis, describing the situation at attempted coup.

Ukrainian opposition leader and former interior minister Yuriy Lutsenko has said the country's security services are investigating him for an alleged attempt to "overthrow the state".

Lutsenko, a close ally of jailed pro-Western former prime minister Yulia Tymoshenko, is a key figure in the protest movement locked in a two-month confrontation with Ukraine's President Viktor Yanukovych.

EU Enlargement Commissioner Stefan Fuele said Wednesday he will return to the Ukrainian capital next week to continue efforts to help defuse the country's crisis.

"The European Union stands ready to assist all sides," Fuele told the European Parliament, adding that he and EU foreign policy chief Catherine Ashton "are working as a team on Ukraine".

The European Union's foreign policy chief Catherine Ashton said on Wednesday that Brussels was ready to provide support for Ukraine's constitutional reform plans and help investigate alleged abuses committed during two months of protests.

"We have the capacity to provide support," Ashton told reporters after holding talks with Ukrainian President Viktor Yanukovych.

EU foreign policy chief Catherine Ashton met Ukrainian President Viktor Yanukovych on Wednesday in a fresh effort to resolve a two-month crisis as lawmakers battled over a deal to curb the president's powers.

Buoyed by support from Western dignitaries including the EU's Ashton, the opposition has accused Yanukovych of dragging his feet over proposals to end the worst standoff in Ukraine's history since the fall of the Soviet Union.

U.S. Vice President Joe Biden urged Ukrainian President Viktor Yanukovych Tuesday to pursue dialogue and compromise to end the country's crisis as he called for the "immediate" pulling back of riot police.

In a phone call, Biden "emphasized that the only viable path to peace and stability in Ukraine is through continued dialogue and genuine compromise to form a new government that can earn the confidence of the Ukrainian people," the White House said in a statement.