TEHRAN, Iran — Iran's supreme leader on Saturday backed President Hassan Rouhani's overtures to the West but criticized some aspects of the U.N. visit during which he spoke with U.S. counterpart Barack Obama.

The comments were the first public response by Ayatollah Ali Khamenei, who wields ultimate authority in Iran, to Rouhani's opening to the West in New York last week, which was capped by the historic 15-minute telephone conversation with Obama.

"We support the diplomatic initiative of the government and attach importance to its activities in this trip," Khamenei told military commanders and graduating cadets in remarks reported by his website, Khamenei.ir.

However he added — without elaborating — that "some of what happened in the New York trip was not appropriate . . . although we trust in our officials."

The telephone conversation on Sept. 27 was the first diplomatic contact between Iranian and U.S. presidents since the 1979 Islamic revolution.

For Khamenei, who has the final say on all matters of state including foreign policy, the suspicion runs deep.

"We are pessimistic towards the Americans and do not put any trust in them. The American government is untrustworthy, supercilious and unreasonable, and breaks its promises," he said.

Rouhani's visit to New York for the U.N. General Assembly came after Khamenei had given the government permission to show "heroic flexibility," raising Western hopes of a breakthrough in long-troubled talks on Iran's nuclear program.

"Heroic flexibility is very useful and necessary sometimes but with adherence to one main condition," Khamenei had told members of the elite Revolutionary Guards on September 17.

"A wrestler sometimes shows flexibility for technical reasons. But he does not forget about his opponent nor about his main objective," he said then.

There has also been public criticism of the Rouhani-Obama phone conversation from the Guards, which regards itself as the defender of the values of the revolution.

Its commander Gen. Mohammad Ali Jafari said the Iranian president should have waited for U.S. concessions before agreeing to the call.

But he too voiced broad support for Rouhani's "firm and appropriate position," adding that "tactical errors" could be "repaired."

In addition to Rouhani's phone call, Foreign Minister Mohammad Javad Zarif met U.S. Secretary of State John Kerry in New York for talks between Iran and the major powers on its nuclear program.

Rouhani has vowed to take a more constructive approach to the talks in a bid to win relief from crippling U.S. and European Union sanctions on Iran's oil and banking sectors.

Representatives of Iran and the six powers are to meet in Geneva later this month to seek ways to jumpstart the decade-old negotiations that were put on hold in April ahead of the presidential election in which Rouhani won a surprise first-round victory.

Khamenei on Saturday also hit out at Washington for its alliance with Iran's number one foe, Israel.

The American administration "is a government that is seized by the international network of Zionism, and has to put up with the usurper (Israeli) regime and show flexibility towards it," Khamenei said.

Israeli Prime Minister Benjamin Netanyahu secured a tougher line from Obama in his public comments after their White House talks last Monday, sparking Iranian accusations of "flip-flop" by the US president.

Obama said Rouhani's overtures would be judged on actions and not words, adding that the use of military force was still on the table.

In his address to the U.N. General Assembly last Tuesday, Netanyahu went on to warn that Israel was ready to act alone in taking military action to prevent any possibility of Iran developing a nuclear weapons capability.

Khamenei said any such action would be met with a "harsh" response.

"We hear the repetitive and disgusting threats of the Iranian nation's enemies. Our response to any mischief will be serious and harsh," he said.

Iran has warned in the past that any attack against its soil would provoke retaliation against the Jewish state and against U.S. bases and warships in the region.