Though oil and gas are on the agenda, an aide to the Kremlin said work on nuclear energy was one of the more important issues during talks Friday with Iran.

Iranian President Hassan Rouhani met Friday with Russian President Vladimir Putin on the sidelines of a regional multilateral meeting of the Shanghai Cooperation Organization in Tajikistan.

Yuri Ushakov, an adviser to the Russian president, said both sides would discuss Russian supplies of oil, gas and energy equipment to Iran. The two leaders, however, would focus on "the most important aspects of cooperation in the peaceful use of nuclear energy," he said Friday.

Russia supplies nuclear fuel to Iran's nuclear reactor in Bushehr.

Both sides have mulled an oil-for-goods deal that would give Iran an opportunity to circumvent international sanctions on its energy sector. The U.S. government said it would act should such a deal emerge, but said so far it's nothing more than a rumor.

Bilateral trade between Russia and Iran was $1.6 billion last year, a 31.5 percent decline from the previous year. The Kremlin attributes the drop to sanctions on Iran.