MOSCOW (Reuters) - Progress at talks between world powers and Iran on its nuclear program later this month will depend on the United States showing "genuine honesty and goodwill", the Islamic Republic's ambassador to Russia said on Wednesday.

The two sides will meet in Kazakhstan on February 26 in another effort to forge a deal on Iran's nuclear ambitions. Iran says it wants only peaceful energy from nuclear fuel while the powers suspect it is pursuing the means to develop nuclear weapons.

Previous attempts have failed to yield an overall agreement on curbing and monitoring Iran's nuclear activities and hopes of success at the next talks have been tempered by signs of skepticism in Tehran.

But a senior Russian official said he hoped progress was possible and Iran's ambassador to Russia, Mahmoud Reza Sajjadi, said the ball was in Washington's court.

"If they (the United States) demonstrate genuine goodwill and honesty, we'll have the best possible talks," the envoy told a news conference in Moscow, sitting in front of a screen showing a montage of Iranian cultural and sporting achievements.

He echoed Iran's foreign minister in welcoming U.S. Vice-President Joe Biden's offer of bilateral talks on Saturday, but in other comments the ambassador sought to cast doubt on the trustworthiness of Washington.

"Our attitude to this proposal is positive ... but I ask you Russians, how much do you believe Americans?" Sajjadi said. "Obama said America would not let Israel build new settlements (in occupied territory) ... Did they keep their word?"

Western diplomats say Iran has avoided addressing their concerns in previous rounds talks to buy time to develop nuclear technology with potential civilian or military applications.

The talks this month in the Kazakh city of Almaty will bring together officials from Iran as well as the United States, Russia, China, France, Britain and Germany.

Russia has supported four rounds of U.N. Security Council sanctions against Iran but criticized unilateral European Union sanctions including an oil embargo, imposed on Tehran.

A senior Russian diplomat said he hoped the negotiations would be productive because time was running out.

"In spite of everything I hope the next round of talks leads, if not to a breakthrough, then to a serious change ... a lot of time has been wasted," Deputy Foreign Minister Sergei Ryabkov told state news agency Ria.