NEW YORK—Iran's President Mahmoud Ahmadinejad arrived in New York early Sunday for the United Nations General Assembly this week and said in an interview on ABC's "This Week" that he considered the release of the American hiker, Sarah Shourd, a huge humanitarian gesture and hoped the U.S. would free Iranians detained here.

Mr. Ahmadinejad denied he was offering to exchange prisoners but said the eight Iranians jailed in the U.S., some on charges of flouting international sanctions, were being held illegally.

Meanwhile, Ms. Shourd, 32 years old, who was released last week from detention in Iran after 13 months, held a news conference in New York on Sunday afternoon, saying she felt only "one-third free" because her two American fellow hikers—her fiancé, Shane Bauer, and their friend Josh Fattal—were still in detention.

The three Americans were arrested in July 2009 for illegally entering Iran's border from northern Iraq and have been formally charged with espionage.

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.Ms. Shourd said she didn't "in any way blame the Iranian people," whom she praised for their "noble Islamic values" and their "fervent worship of God."

She also praised President Ahmadinejad and the Ayatollah Ali Khamenei, Iran's supreme leader, for her "compassionate release."

She said she hoped their gesture didn't go "unrecognized" and that the incident would foster better understanding between the U.S. and Iran.

"Shane and Josh do not deserve to be in prison one day longer than I was," Ms. Shourd said. "We committed no crime and we are not spies. We in no way intended any harm to the Iranian government or its people and believe a huge misunderstanding led to our detention and prolonged imprisonment."

In his interview with Christiane Amanpour on "This Week," broadcast Sunday morning, Mr. Ahmadinejad said the case was being investigated and didn't say whether the other two hikers, both 28, would be released.

Mr. Ahmadinejad also denied that tough economic sanctions imposed by the U.N and the international community over Iran's nuclear program were having an effect on Iran's economy.

He said Iran took the sanctions seriously, but that the country could overcome them.

"None of this is a problem. I want to stress this is not a problem. If you want to say it's effective, why not wait for the next six months or a year and see with your own eyes whether there are effects or not," said Mr. Ahmadinejad.

U.S. Secretary of State Hillary Clinton gave a separate interview to Ms. Amanpour and reiterated her belief that Iran had moved from an Islamic Republic state to one that was ruled by a military dictatorship, under the political and economical influence of the Revolutionary Guards Corps.

Ms. Clinton said the sanctions were having an impact.

"The information we're getting is that the Iranian regime is quite worried about the impact on their banking system, on their economic growth, because they've already encountered tough economic times, and this is making it more costly," Ms. Clinton said.

Mr. Ahmadinejad met on Sunday with U.N. Secretary-General Ban Ki-moon to discuss developments in Iraq, Afghanistan and the Middle East, as well as efforts to resolve the dispute over Iran's nuclear program, according to news reports.

Iranian opposition supporters of the Green Movement planned protest rallies in New York on Thursday when Mr. Ahmadinejad is scheduled to address the General Assembly.