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Iranian President Mahmoud Ahmadinejad's planned four-nation tour of Latin America is a sign of desperation as sanctions increasingly isolate his country, the Obama administration said Friday, as it warned the leader's hosts against expanding ties with Iran.

The State Department dismissed Ahmadinejad's visits to Venezuela, Nicaragua, Cuba and Ecuador next week as Iran "flailing" for new friends as the sanctions bite. Some lawmakers have expressed deep concern that Iran is boosting its presence in the Western Hemisphere to the detriment of U.S. national security interests.

"As the regime feels increasing pressure, it is desperate for friends and flailing around in interesting places to find new friends," State Department spokeswoman Victoria Nuland told reporters. "We are making absolutely clear to countries around the world that now is not the time to be deepening ties, not security ties, not economic ties, with Iran."

"Rather, it's in the entire international community's interest to make clear to Iran that it's got a choice," she said. "It can remain in an international isolation, or it can comply with its obligations and start cooperating and rejoin the community of nations."

Nuland said Iran must stop defying international pressure to prove that its nuclear program is peaceful and that countries must make it clear that the only way to end its isolation is to come clean about its atomic ambitions. The U.S. and its allies accuse Iran of trying to develop atomic weapons under the cover of a civilian nuclear energy program. Iran denies the charge.

Ahmadinejad has courted leftist, populist and anti-U.S. Latin American leaders for some time, notably Venezuelan President Hugo Chavez and Nicaraguan President Daniel Ortega. During his stop next week in Managua, Ahmadinejad is to attend Ortega's inauguration. The U.S. will be represented at the ceremony by a mid-ranking diplomat from the U.S. embassy, officials said.

Ahmadinejad visit to Washington's backyard has raised eyebrows in Congress where the chairwoman of the House Foreign Affairs Committee, Rep. Ileana Ros-Lehtinen, a Republican, likened it to a "tour of tyrants" that is proof of Iran's expanding interest in the region.

"Ahmadinejad's desire to strengthen ties with anti-American dictators and expand Iranian influence in the Western Hemisphere directly threatens U.S. security interests," she said in a statement.

"This is a threat which we cannot ignore," Ros-Lehtinen said, pledging to hold hearings on the matter to discuss what the administration is doing to counter Iranian outreach in the Western Hemisphere.