Brussels said Monday Greece and its eurozone partners were accelerating their talks but had "lots of ground to cover" before April 20 when Athens must release a list of reforms aimed at unlocking key aid funds.
"Right now these discussions are gaining speed but time is running out," Valdis Dombrovskis, the European Commission vice-president for the euro, told Bloomberg TV.
"So there is still lots of work to do, lots of ground to cover until April 20th which is more or less preliminary date when one should (present) some Greek list of reforms," he added.
Greece's eurozone partners have given Athens until next Monday to present a list of acceptable reforms in exchange for the final tranche of aid funds promised under a multi-billion-euro bailout, or 7.2 billion euros.
The issue is due to be discussed among eurozone finance ministers when they meet in Riga on April 24.
Dombrovskis declined to say whether the amount would be decided during the meeting in Latvia, saying: "It really depends how the technical negotiations will go."
He added: "There is also more time for negotiations but Greek authorities are emphasising that the cash position is getting more difficult."
Dombrovskis, a former Latvian prime minister, has taken a hard line against Greece within the European Commission, the executive of the 28-nation European Union.
"There is no secret that those negotiations are very complicated. There were lots of unhelpful rhetoric, but we are willing to work with the Greek government and to arrive at a positive result," he said.