BRUSSELS (REUTERS) - Greece has three days to reassure its lenders it can deliver on conditions attached to its international bailout in order to receive the next tranche of aid, four euro zone officials said on Tuesday.

Athens and its creditors unlocking 8.1 billion euros (S$13.4 billion) of rescue loans resumed talks on Monday on after a two-week break during which the government almost collapsed over redundancies at state broadcaster ERT.

There is a general dissatisfaction with progress in Greece when it comes to reforming its public sector, such as tax and custom collection or health care services, a senior euro zone official involved in negotiations said.

"All agreed that Greece has to deliver before the Eurogroup on Monday. That's why they must present again on Friday," a second source told Reuters.

Euro zone finance ministers are scheduled to meet on July 8 and discuss the situation in Greece.

To pressure Athens to deliver on reforms, its EU/IMF lenders might refuse to pay the full sum in one go and break it up into three monthly payments instead, Greek media reported.

"It is a very difficult negotiation," a senior Greek official participating in the talks said. "We're moving fast to wrap up as many issues as possible a soon as possible."