LAUSANNE, Switzerland — Iran and six world powers are close to a nuclear agreement and are expected to iron out most of their remaining differences by the weekend, but another round of talks likely will be needed to seal any deal, a senior Russian official said Friday.

Senior Russian negotiator Sergey Ryabkov told The Associated Press that while some differences remain, negotiators are expected to “finish their main work” by Saturday, with another session likely next week, he said.

Other diplomats said the current session could end even earlier, with the Iranian delegation departing for home to allow Foreign Minister Mohammad Javad Zarif and others to attend the funeral of the mother of Iranian President Hassan Rouhani, who died earlier this week. The diplomats insisted on anonymity because they were not allowed to divulge details of the talks.

Ryabkov’s comments jibe with that of other officials who told the AP earlier that the United States and Iran are drafting elements of a deal that commits Tehran to a 40 percent cut in the number of machines it could use to make an atomic bomb. In return, the Iranians would get quick relief from some crippling economic sanctions and a partial lift of a U.N. embargo on conventional arms.

Agreement on those details of Iran’s uranium enrichment program could signal a breakthrough for a larger deal aimed at containing the Islamic Republic’s nuclear activities.

Iran is negotiating in Switzerland with the United States, Russia, China, Britain, France and Germany, with an end-of-March deadline to reach a preliminary deal for Iran to scale back its nuclear program in return for an easing of economic sanctions. Iran insists it is not trying to build a nuclear bomb, but the West is skeptical.

The sides ultimately want to reach a full agreement by the end of June. In Brussels, French President Francois Hollande, British Prime Minister David Cameron and German Chancellor Angela Merkel discussed the state of negotiations Friday with the EU’s top diplomat, Federica Mogherini. Ryabkov said earlier that foreign ministers of those three nations were considering joining the talks in Lausanne, but as the day advanced ”“ and it appeared that the Iranians might leave by Saturday ”“ other diplomats said that was no longer likely.

The negotiations build on a deal struck in late 2013 that commits Tehran to temporary restrictions while the present negotiations continue. A confidential International Atomic Energy Agency report issued Friday and shared with the AP said Iran was honoring those commitments.