Greece's combative finance minister has indicated that Athens' new radical left government is prepared to put some of its campaign promises on hold while it seeks to build confidence among its creditors.

"Our program is a program for four years," Yanis Varoufakis told reporters after a meeting of economic and finance leaders in northern Italy on Friday.

Argentina threatened Friday to revoke Citibank's operation license if it refuses to process payments to bondholders, a move ordered by a New York judge presiding over a long fight between the country and a U.S. investment group.

In a statement, the Ministry of Economy said failure to process the payments could lead to criminal charges against Citibank's employees in Argentina. The warning came a day after U.S. District Judge Thomas Griesa told Citibank that it cannot let its Argentine branch process payments to bondholders unless U.S. investors are paid as well.

Schools, hospitals, courts and state offices across Portugal were hit by a day-long strike on Friday called by civil servants fed up with austerity-linked salary and job cuts.

Banners were put up in front of many institutions proclaiming "closed due to the strike". The protest was called by federations linked to the two main trade unions, the CGTP and UGT.

EU Commission chief Jean-Claude Juncker has warned of an alarming lack of progress in talks on Greece's bailout, as Germany raised the spectre of a tumultuous Greek exit from the euro.

Juncker was meeting Alexis Tsipras, the leader of the hard-left Syriza party who came to power in January, on Friday just days after Tsipras renewed a demand that powerful Germany repay debts from its Nazi past.

A recent rebound in oil prices is built on flimsy foundations, the International Energy Agency warned Friday, with another sharp fall possible and few signs that cheap fuel was giving growth a real boost.

Oil prices plummeted by 60 percent between June and January, but have since come off six-year lows and stabilised somewhat, with London's benchmark Brent trading around $60 per barrel and WTI in the United States fluctuating around $50 per barrel.

EU Commission chief Jean-Claude Juncker complained Friday about a lack of progress in talks on Greece's bailout, but insisted there was no chance of a failure that could drive the country out of the eurozone.

"I am not satisfied by the developments in the recent weeks. I don't think we have made sufficient progress, but we will try to push in the direction of a succesful conclusion of the issues we have to deal with," he said ahead of talks with Greek premier Alexis Tsipras.

Cyprus will not need all of the 10-billion-euro bailout it received in 2013 as its economy recovers faster than expected, the country's finance minister told Agence France Presse.

"(The economy) is much better, but I'm not saying that it is good," Harris Georgiades said ahead of the second anniversary of the "unprecedented crisis" that shook the eurozone and left the Mediterranean island teetering on the brink of bankruptcy. 

Three major U.S. daily newspapers announced plans Thursday to make their articles available through a Dutch-based startup pioneering the use of "micropayments" for news.

The New York Times, The Wall Street Journal and The Washington Post agreed to work with Blendle, which describes itself as a "digital newsstand" allowing readers to buy individual articles online, according to a joint statement.

China is in talks with the International Monetary Fund for the Washington-based institution to add the yuan to its basket of reserve currencies, a top banking official said Thursday as Beijing seeks a greater global role for the unit.

It hopes the yuan will become part of the IMF's "special drawing rights" (SDR) assets "in the foreseeable future", said vice central bank governor Yi Gang.

Greece and its international creditors were to begin fiscal talks in Athens on Thursday, with technical experts getting to grips on drawing up a new economic plan for the troubled eurozone nation.

Finance Minister Yanis Varoufakis said a "fact-finding mission" would gather data to assist the talks held in Brussels.