Oil prices have dropped due to awaited talks on an Iranian nuclear deal to allow the country to restart fuel exports, adding to crude’s total supplies.

Brent crude for August declined 20 cents at $63.00 a barrel, while the US crude slipped 25 cents at $59.45 a barrel, Reuters reported.

Oil traders believe that Iran signing an agreement with Western powers to put an end to economic sanctions will allow the oil rich country to resume exports, which could add to the oversupplied market.

"If they spring a deal, that would be taken as a bit of a surprise."

Oil traders are also keenly watching last-minute negotiations that are in progress to try to avoid a Greek debt default.

According to economists, such default may give strength to the dollar against Euro, which will make commodities including oil dearer for holders of other currencies.

Saxo Bank senior commodity strategist Ole Hansen told the news agency: "If they spring a deal, that would be taken as a bit of a surprise."

Commerzbank Frankfurt energy analyst Barbara Lambrecht said that the Iranian nuclear deal may not be concluded by the deadline and there are chances that it may be delayed.

A self-imposed deadline of 30 June has been set to put an end to the negotiations, which have been taking place for the past two years and are aimed at limiting Iran’s nuclear programme in return for sanctions relief.