After decades of animosity and false starts, the United States and Iran may be best advised to go slow in their effort to repair relations, experts say.

The US and Iranian top diplomats will meet Thursday for one of the countries' highest-level interactions since the 1979 Islamic revolution to discuss Tehran's disputed nuclear program.

But all sides have been quick to say that the encounter, which will also include European, Russian and Chinese foreign ministers, will be brief and not solve the long standoff over Iran's nuclear work.

And after days of speculation that Iran's new President Hassan Rowhani would meet or at least shake hands with President Barack Obama at the United Nations, a US official said that the White House reached out and concluded that the Iranians were not ready.

"My sense is the flirtation has begun and now everybody is waiting for the first big kiss but that's probably not going to come anytime soon," said John Tirman, executive director of the Center for International Studies at the Massachusetts Institute of Technology.

Both Obama and Rowhani "are conscious that a better relationship is not going to be assured through speeches at the UN but rather through negotiations," Tirman said.

Tirman said that arms control negotiations historically required several months and that the two sides were mindful of historical lessons.

Iran's clerical regime sees hostility to the United States as a core value of the 1979 revolution, which ousted the Western-oriented shah.

Mohammad Khatami, who rose to the presidency in 1997 on a reformist platform, faced a major backlash from hardliners who say him as moving too quickly.

Rowhani was elected in June on promises to ease tensions with the West and repair an economy crippled by US-led sanctions.

Rowhani, who had heavily promoted his UN debut through US media appearances, appealed for Obama to ignore "warmongering pressure groups" to make peace and vowed that Iran did not want nuclear weapons.

But Rowhani also offered a firm defense of the clerical regime's core principles as he denounced the domination of the West and its "strategic violence" in the Middle East.

Karim Sadjadpour, an expert on Iran at the Carnegie Endowment for International Peace, said that Rowhani needed to ensure the support of Iran's supreme leader, Ayatollah Ali Khamenei.

"For the last few weeks Rowhani's charm offense seemed intent on impressing Obama, but his UN performance seemed more intent on reassuring Khamenei that he would not deviate from revolutionary ideals," Sadjadpour said.

"Shaking hands with Obama would have won Rowhani huge points with the Iranian public, but it would have caused Iran's hardliners to have a conniption," he said.

Sadjadpour said that, so long as the 74-year-old Khamenei remains in charge, Rowhani and his US-educated foreign minister -- Mohammad Javad Zarif, who meets Thursday with John Kerry -- were likely to be the Iranians most likely to strike a deal.

Similarly, the Obama administration has repeatedly shown interest in improving relations with Tehran but must be mindful of the US Congress, which moved to slap new sanctions on Iran days before Rowhani's inauguration.

"For a deal to be reached, the most important gap that needs to be bridged is not between Rowhani and Obama, but between the US Congress and Khamenei," Sadjadpour said.

Obama in his own speech offered reassurances to Israel, which has been deeply suspicious of Iran and was outraged by the Holocaust denial of Rowhani's predecessor Mahmoud Ahmadinejad.

Prime Minister Benjamin Netanyahu, who has not ruled out a military strike on Iran, instructed Israel's delegation to boycott Rowhani's speech which he later called "full of hypocrisy."

Hussein Ibish, a senior fellow at the American Task Force on Palestine, said that Iran and the United States had a shared interest on the nuclear issue.

Obama, facing debacles in Syria and Egypt, is eager for diplomatic solutions, while Iran obviously does not want to be attacked.

"I don't think what we are looking at is a process which is going to lead to a rapprochement or long-term resolution of the nuclear weapons issue," Ibish said.

"I think we are looking at a grand postponement. It is in the interest of both sides for the next three or four years not to have a confrontation on this issue," he said.