The head of the U.N. nuclear watchdog agency said Friday he will travel to Iran over the weekend on a previously unscheduled visit to try to resolve an impasse over access to Iranian nuclear documents and scientists.

The visit to Tehran by Yukiya Amano, director general of the International Atomic Energy Agency, is set for Sunday, three days before the start of a closely watched round of nuclear talks between Iran and six world powers, including the United States.

A three-sentence statement by the nuclear agency said only that Amano would “discuss issues of mutual interest with high Iranian officials” during his visit. Among the expected participants was Saeed Jalili, the secretary of Iran’s Supreme National Council and the country’s chief nuclear negotiator, the IAEA said.

The surprise visit follows two days of reportedly successful technical discussions at the IAEA’s Vienna headquarters on a formula for clearing up a dispute over controversial nuclear research projects conducted nearly a decade ago by Iranian scientists. IAEA officials, citing documents and other evidence, say Iran appears to have conducted extensive research until at least 2003 on the design and testing of nuclear warheads.

Iran denies having ever worked on nuclear weapons and claims that the documents were forgeries. Yet Iranian officials have refused to answer specific questions or to make key scientists available for interviews.

Diplomats knowledgeable about Amano’s visit said the IAEA chief hoped to win Iranian support for a plan that will spell out how the two sides would work together to clear up lingering questions about past nuclear research. But even if the plan is approved, the officials say, the more important test will come later, when Iran is asked to grant the IAEA access to key personnel as well as to military sites where the research was allegedly conducted.

Jalili, in remarks broadcast on Iranian television, said Thursday that Iran was ready to negotiate seriously to resolve questions about the country’s nuclear program. But he cautioned Western governments to back off from threats of military and economic pressure.

“Statements of some Western officials . . . were a mistake,” Jalili told the Iranian news channel IRINN. “It is important so that these mistakes would not repeat in the future.”

The flurry of diplomatic activity came as Israeli officials continued to raise doubts about Iran’s willingness to meet international demands to scale back its nuclear ambitions. Israeli Prime Minister Benjamin Netanyahu told reporters Friday that he saw no evidence of sincerity on Iran’s part.

“It looks as though they see these talks as another opportunity to deceive and delay, just like North Korea did for years,” Netanyahu said.