Germany said Friday it expects Athens to implement reforms agreed under a massive bailout, as Greek Prime Minister Alexis Tsipras's resignation has not changed anything agreed under the European rescue plan.

"The programme was agreed with the Greek government, and that runs on for three years. That has not changed," Steffen Seibert, spokesman for Chancellor Angela Merkel, told reporters.

"The federal government, like all other European governments, expects the implementation of reforms, the implementation of the agreement in the programme," he added.

Germany also warned that any delays in putting in place reforms could lead to delays of the next payment of aid funds out of the 86-billion-euro ($96-billion) package.

"We expect the agreed reforms to be implemented in the autumn. If there are delays ... that would also mean the next payment would be delayed," said finance ministry spokesman Juerg Weissgerber.

The European creditors are expected to carry out their first review of the implementation of reforms in October.

Tsipras on Thursday announced his resignation and called for snap elections, as he went on the offensive to defend the bailout after it triggered a rebellion within his own hard-left party.

The Greek premier did not give a date for the new polls but they are expected to be held on September 20, the state news agency ANA said, citing government sources.