GENEVA — A senior U.S. diplomat and Iran’s chief nuclear negotiator met one on one Thursday in Geneva in what appeared to be the highest-level official contact between the countries since Iran’s 1979 Islamic revolution.

The meeting between Undersecretary of State William Burns and the Iranian, Saeed Jalili, took place during a break in negotiations at a villa outside Geneva among the United States, Iran and five other nations.

It was announced by State Department spokesman Robert Wood, who offered no other details.

Senior U.S. officials had said Wednesday that they’d use the sessions in Geneva to press Iran to pull back on its nuclear development program, which Western governments charge is aimed at fashioning a nuclear weapon.

The Burns-Jalili encounter is the latest attempt by the Obama administration to engage Iran, which Washington also has threatened with “crippling” sanctions if it doesn’t suspend the nuclear work.

The State Department allowed Iran’s foreign minister, Manoucher Mottaki, to visit Washington on Wednesday, waiving regulations that usually confine Iranian diplomats within a 25-mile radius of downtown Manhattan. Mottaki didn’t meet with U.S. officials but visited Iran’s interests section, which is overseen by Pakistan, because the United States and Iran have no diplomatic relations.

The United States broke off diplomatic ties with Iran in early 1980, soon after radical students seized the U.S. Embassy in Tehran in November 1979 and took American diplomats hostage.

There have been sporadic U.S.-Iranian contacts in the ensuing three decades, official and unofficial, secret and overt.

Then-U.S. Ambassador to Iraq Ryan Crocker met several times in Baghdad with Iranian representatives in 2007 and 2008 to discuss security in Iran, but those talks included Iraqi officials. Then-Secretary of State Madeleine Albright joined her Iranian counterpart to discuss Afghanistan in 2000, but officials of other countries attended that session, too.

Earlier on Thursday, a Western diplomat, briefing reporters on the condition of anonymity because the talks were ongoing, said that at the morning session, representatives of the six nations told Jalili that Iran must agree to negotiate over its nuclear program.

They reiterated that a June 2008 offer of improved economic, political and security ties remains on the table, the diplomat said.

Iran at times has ruled out talks on its nuclear work, which it says is its sovereign right, and at other times has said it will discuss the issue only in the context of its regional and global concerns.

After all sides read prepared talking points Thursday morning, Jalili “started talking about the nuclear issue in this wider context,” the diplomat said.

The talks are taking place at the Villa le Saugy, outside Geneva. According to an official at the talks, who asked not to be named because the official wasn’t authorized to talk to journalists, the Iranian officials and other delegations “dined and mingled” over an outdoor lunch. The menu included trout almondine, creme brulee, wine and coffee.