Virginia Mayo, Associated Press
European Council President Donald Tusk speaks during a media conference at an EU summit in Brussels on Thursday, March 19, 2015. Ukraine is urging the European Union to stay united on keeping up sanctions pressure on Russia over the conflict in eastern Ukraine as EU leaders gather for a two-day summit.

BRUSSELS — German Chancellor Angela Merkel said Thursday that Greece has no choice but to carry out economic reforms if its wants to receive more financial aid, dashing any hopes Athens might have had for a softening in Berlin's stance.

Tensions over Greece's massive financial bailout overshadowed a European Union summit amid fears that the country could accidently drop out of the euro, triggering a crisis across the currency zone shared by 19 nations.

"There can only be a solution on the basis of the agreements reached in the eurogroup," Merkel said, referring to the meeting last month of finance ministers from the countries that use the euro.

Before Greece receives further rescue loans it must submit a detailed list of reforms, but the radical left-led leadership in Athens has been slow to come forward with new ideas.

A last-minute meeting of select leaders has been added to the European summit agenda for late Thursday to discuss the situation in Greece. Apart from Merkel and Greek Prime Minister Alexis Tsipras, the meeting will include French President Francois Hollande, European Central Bank President Mario Draghi and EU President Donald Tusk.

"Nobody wants a so-called Grexit and everybody wants to avoid this risk," said Tusk. He cautioned against high expectations. "It will not be a decisive meeting."

Merkel agreed, stressing that "it's absolutely clear that nobody can expect a solution for Greece's problems tonight" or on Monday, when she hosts Tsipras in Berlin.

Greek Deputy Prime Minister Giannis Dragasakis said Tsipras would come to Brussels "with specific proposals."

"We are ready to discuss specific reforms that have been cost accounted for, and will soon be more specific about what changes can be made."

Contrasting the economic recoveries in Spain and Ireland with the situation in Greece, Merkel said Athens could only expect further outside aid if it undertakes a "huge effort" of its own.

Merkel cautioned that the stakes were high for everyone, not just Greece, repeating her warning that "if the euro fails, so does Europe."

Her concerns echoed those of the European Union's economics and financial affairs chief Pierre Moscovici, who said that "a Grexit would be more than severe damage."

"If one leaves, the question is: who is next?" he said.

Lorne Cook from Brussels and Derek Gatopoulos from Athens contributed to this report.