A handout picture released by the official Web site of Iran’s supreme leader, Ayatollah Ali Khamenei, shows him delivering a speech during a visit to the Military College of Tehran on October 5, 2013. (Handout/Khamenei.ir/AFP/Getty Images)

The Islamic republic’s supreme leader, Ayatollah Ali Khamenei, lauded President Hassan Rouhani on Saturday for his diplomatic achievements at the U.N. General Assembly last week but reiterated his skepticism about possible negotiations with Washington.

“We support the diplomatic approach of the government and consider diplomatic efforts as important and support what happened in the latest trip,” Khamenei said in his first remarks since Iran’s delegation returned from New York.

At the end of his visit, Rouhani spoke briefly by phone with President Obama, the first direct communication between an Iranian leader and a U.S. leader since Iran’s revolution and the founding of the Islamic republic in 1979. The conversation raised prospects for renewed relations between the two countries.

But Khamenei stopped short of endorsing rapprochement with Iran’s longtime foe.

“We are pessimistic about Americans and have no trust in them. The American government is untrustworthy, disloyal, considers itself superior and breaks its promises,” he said.

“Of course, I do not approve of some of what happened in New York,” he added. “But I am optimistic about the diplomacy of our esteemed government.” Khamenei was apparently signaling his disapproval of the phone call, which took place as Rouhani was headed to the airport for his return flight to Tehran. The call, which Obama initiated, has been hailed as a historic shift in relations between the two countries.

The short conversation was the culmination of a diplomatic outreach effort by Rouhani and his foreign minister, Mohammad Javad Zarif. Iran’s delegation made numerous media appearances in New York, attempting to erase the negative impression made by Rouhani’s predecessor, Mahmoud Ahmadinejad, who used his General Assembly appearances to question the Holocaust and the Sept. 11, 2001, attacks.

Khamenei’s remarks, made at a graduation ceremony at the air force academy, offered a glimpse of the difficult path ahead for Iran and the United States if they are to mend relations and begin direct negotiations over Iran’s nuclear ambitions, the crisis in Syria and other regional issues that concern both Washington and Tehran.

On Thursday, Wendy Sherman, the State Department’s undersecretary for political affairs, asked Congress to delay sanctions on Iran until after the next round of negotiations between Iran and world powers in Geneva later this month.

But in a reference to Iranian officials, she also said that “deception is part of the DNA.”