The troika of international lenders still has many open questions regarding debt-laden Greece to resolve before reaching an agreement on the payment on the next tranche of aid to the country, a German government official said on Thursday.

The official said that Greece would not be a central topic of the meeting of Group of 20 leading economies in Mexico this weekend but it would likely be discussed on the sidelines.

"There are still open questions, a whole series of open questions regarding Greece within the Troika, but then also within the Eurogroup,» said the official.

The official said that Germany would ask the United States again how it was planning to do about its so-called «fiscal cliff» but was braced for the answer again that this could not be resolved until after the presidential elections.

The U.S. said on Wednesday that the nation would hit the legal limit on its debt near the year's end.

"You understand that from a European view, these are important questions also for the world economy that we want to factor out,» the German government official said.

"We are prepared to talk about our topics transparently but, please, we expect the same also from our European and our international partners."

The Mexico City meetings of G20 finance ministers and central bank governors follow talks in Tokyo more than two weeks ago, which endorsed a checklist of policy reforms aimed at pressuring Europe and the United States to tackle their debt troubles. [Reuters]