Jeroen Dijsselbloem, who heads the group of euro zone finance ministers, said Greece must meet its obligations and agreements if it wants to remain in the currency bloc. But he also said that a Greek exit was "not an option".

If Greece leaves "the euro zone you (would) get very dangerous instability," Dijsselbloem told broadcaster RTL. "It's in the interests of Greece and the euro zone as a whole to avoid that."

Greece is locked in negotiations with its international lenders. It risks running out of cash within weeks if it fails to strike a deal to unlock fresh bailout funds and is tapping into public cash reserves to meet immediate obligations.

"The money is starting to run out," Dijsselbloem said.

Greek Prime Minister Alexis Tsipras is due to present plans to reform Greece's economy before a meeting of euro zone finance ministers in Riga on April 24. He hopes to secure the release of bailout funds to prevent a default which could trigger a 'Grexit' or Greek exit from the euro.

Dijsselbloem said that if Greece wants to remain in the euro zone "it must meet certain conditions and agreements so we can reach a deal."

(This version of the story was refiled to correct a typo)

(Reporting By Toby Sterling; Editing by Susan Fenton)