Greece's international lenders have demanded additional details on Athens' proposals in an austerity package worth nearly €12 billion, the finance minister has said.

"There are discussions on the measures. The troika wants clarifications," Yannis Stournaras told reporters after the latest round of talks between the government and its European Union and IMF lenders.

Greece's brutal recession is set to extend into a sixth year in 2013, when the economy will contract by another 3.8%.

This is according to forecasts in the draft budget submitted to Parliament today.

This year's recession will see the economy shrink around 6.5%, the document estimated. Unemployment is predicted to rise to 24.7% in 2013 from an average 23.5% in 2012.

The budget sees Greece's government still running at a loss despite waves of spending cuts and tax hikes over the past two years, as it has struggled to meet the terms for rescue loans from other euro zone countries and the International Monetary Fund.

The deficit for 2012 is expected to stand at 6.6% of GDP, improving slightly to 4.2% - or €8 billion - next year, the document showed.

Greece still has a primary deficit - which excludes interest rates paid on existing debt - of 1.4% of GDP this year, disappointing earlier forecasts for a surplus. That is expected to improve in 2013, when the budget projects a small primary surplus of 1.1% of GDP.

The budget includes about €7.8 billion worth of austerity measures for next year. They are part of a €13.5 billion package of spending cuts and tax hikes for 2013 and 2014 that Greece's international creditors have demanded in exchange for continued payout of the rescue loans that are protecting the country from a messy default.

Of the €7.8 billion in measures for next year, €3.8 billion are to come from pension cuts and €1.1 billion from salary cuts. Other cutbacks include trimming costs for healthcare, education and defence.

Finance Minister Yannis Stournaras submitted the draft budget to Parliament after talks with debt inspection teams from the IMF, European Central Bank and European Commission - known as the troika.

Negotiations with the troika continue on the details of the two-year austerity package, meaning some of the details in the draft budget could be amended. Parliament usually votes on the budget in December.

Austerity talks involving the troika and three political parties backing Greece's four-month-old coalition government have dragged on for weeks, with disagreement over how the cuts will affect low-income Greeks suffering under recession.

Conservative Prime Minister Antonis Samaras, in a weekend newspaper interview, argued the country was showing its rescue lenders that it is serious about its reforms.

"Our partners can see that changes are now happening," Samaras told the Sunday To Vima newspaper. "The first thing we must do is win back our damaged credibility. Without credibility, you can't negotiate," he added.