LONDON: Greece’s new leaders on Monday embarked on a diplomatic campaign to win backing for a renegotiation of a 240 billion euro ($270 billion) bailout, winning support from US President Barack Obama but a stark warning from Britain.

On a European charm offensive in the face of German opposition, Finance Minister Yanis Varoufakis met his British counterpart George Osborne in London, while Prime Minister Alexis Tsipras held talks in Cyprus.

Greek stocks, which have been volatile since the Jan. 25 election won by Tsipras’s left-wing Syriza party, jumped more than five percent after Obama warned that imposing austerity on Greece could backfire on its creditors.

“You cannot keep on squeezing countries that are in the midst of depression,” Obama told CNN.

“At some point, there has to be a growth strategy in order for them to pay off their debts to eliminate some of their deficits.”

Obama said the Greek economy was in “dire need” of reform but warned that drastic changes were tough to implement in a struggling economy.

A source traveling with Finance Minister Varoufakis said the “whole government was very happy” to hear Obama’s comments in the face of hardening rhetoric from austerity proponents.

In Cyprus on his first foreign trip since coming to power, Tsipras said he had not expected so much international support for his campaign and stressed that Greece wanted a wider debate about debt for “all the peoples of Europe.”

“Europe is in crisis, not just Greece and Cyprus,” he said.

He also doubted the legality of the current system of supervision of indebted nations by the so-called “troika” of creditors, the International Monetary Fund, European Union and European Central Bank (ECB).

Tsipras will travel to debt-laden Italy on Tuesday and on to Brussels on Wednesday for talks with European Commission President Jean-Claude Juncker.

In London, British minster Osborne warned that the stand-off between Greece and the eurozone was “the greatest risk to the global economy” but said that he had enjoyed a “constructive discussion” with Varoufakis.

In comments shown on British television, he said all sides should “act responsibly.”

The Greek government source said Varoufakis was “delighted” following the talks, adding: “having a key ally like Britain in the EU is a major asset.”

The Greek minister was later to meet with around 100 figures from London’s financial sector, including investors and bankers exposed to Greek debt.

“We are very open to investment,” stressed the source, who insisted that Greek debt would be serviced “on terms that will have no detrimental effect on private bondholders.”

Varoufakis said Sunday that Greece did not want a promised loan tranche of 7.2 billion euros, saying it would just add more debt to the pile.