Israeli Prime Minister Benjamin Netanyahu on Sunday cast doubts on the conclusion of nuclear talks between world powers and Iran in Istanbul.

"My initial impression is that Iran received a present. It has five weeks in which it can continue to enrich (uranium) without limitations," Netanyahu said at the beginning of a meeting with visiting U.S. Senator Joseph Lieberman in Jerusalem.

Netanyahu reiterated the demands he posed last month for a satisfactory diplomatic resolution to the long-standing dispute over Tehran's nuclear ambitions: an immediate cessation of all uranium enrichment activities, the removal of existing military- grade fuel stockpiles to a neighboring country, and the dismantling of the newly constructed Fordo nuclear research facility near the city of Qom.

"I believe the world's biggest wheeler-dealer of terrorism must not be given the possibility to develop a nuclear bomb," Netanyahu said, referring to Iranian President Mahmoud Ahmadinejad.

The Israeli prime minister's statement came a day after Iran and six world powers -- the United States, Russia, France, China, Britain and Germany -- concluded a new round of negotiations in Istanbul. The talks, the first of their kind in 15 months, ended without a breakthrough, but with an agreement to reconvene a second round in Baghdad on May 23.

During Saturday's talks, the Western countries aimed to persuade Iran to cease the higher-grade uranium enrichment it began two years ago. The European Union foreign policy chief Catherine Ashton, who led the Western delegation, described the talks as "constructive and useful."

However, Israeli officials responded to Ashton's announcement with skepticism, saying that the Iranians were playing for time.

"The Iranians are fooling everyone. It's premature to know whether they are serious," one top official told the Yediot Aharonot daily over the weekend.

"As long as (the Iranians) don't come with a serious proposal, namely a willingness to discuss ending the enrichment at high and low levels and opening all their facilities to IAEA inspection, there won't be a breakthrough. We'll know if it's serious in the next round (of talks) in Baghdad. For now it is only a game of Middle Eastern negotiations," the official added.