House Republicans this week accused Argentina of trying to block their investigation into suspected Iranian ties to terrorism in the Western Hemisphere by refusing to let an Argentinian prosecutor testify on the matter Tuesday.

Lawmakers had invited the testimony from Alberto Nisman, the special prosecutor in the 1994 bombing of a Jewish center in Buenos Aires, in hopes that it would refute the report by the State Department that asserted Iran’s influence in the hemisphere is “waning.”

Mr. Nisman made international headlines in May when he issued a 500-page report claiming that Iran has, in fact, spent the past three decades growing terrorist networks throughout Latin America, infiltrating several nations in the region with the goal of executing future attacks.

Two House Republicans claimed the Argentine government was refusing to allow Mr. Nisman to travel to Washington and appear for Tuesday’s hearing.

Reps. Michael T. McCaul, the chairman of the House Homeland Security Committee, and Jeff Duncan, who is chairman of the subcommittee that was holding the hearing, wrote a letter to Argentina’s President Cristina Fernandez on Monday, bemoaning her government’s move to block Mr. Nisman’s testimony.

Mr. Nisman’s recent report “underscored a critical issue to U.S. homeland security, showing that Iran was ‘the main sponsor’ of an attempted attack in June 2007 on American soil to blow up John F. Kennedy (JFK) airport in Queens, New York,” the lawmakers wrote to the Argentine president.

“Had the plot not been uncovered, an untold number of Americans could have been killed by this terrorist act,” they wrote.

In a statement, Mr. McCaul, of Texas, said Mr. Nisman’s years-long probe into who carried out the 1994 bombing of the Asociacion Mutual Israelita Argentina (AMIA) building in Buenos Aires has shown “the Iranian presence in the Western Hemisphere is greater than we imagined.”

“Iranian infiltration within countries in our region presents a clear and present danger to our homeland, as do attempts to silence or downplay this threat,” said Mr. McCaul.

Argentina’s own relations with Tehran became a subject of scrutiny earlier this year, particularly with the announcement of plans for an Argentine-Iranian “truth commission” designed to get to the bottom of the 1994 bombing.

Messrs. McCaul and Duncan alluded to the “truth commission” in their letter to Ms. Fernandez.

“The government of Argentina has indicated its desire to pursue justice and truth on Iranian involvement” the lawmakers wrote. “However, the decision to deny authorization for Mr. Nisman to testify before the U.S. Congress does call into question the authenticity of your intentions.”

In his own statement, Mr. Duncan said Mr. Nisman’s findings stood in “contrast to the U.S. State Department’s recent assessment that Iran’s influence in Latin America and the Caribbean is ‘waning.’”

“Nisman’s investigation revealed that Iran is deeply embedded within countries in Latin America,” he said.

Mr. Duncan worked last year with Rep. Brian Higgins, New York Democrat, in pushing legislation that mandated the State Department report, which was delivered to Congress last month.

Sources have told The Washington Times the almost entirely classified document concluded that Iran is not supporting active terrorist cells in the Western Hemisphere. While the State Department found the number of Iranian officials operating in Latin America has increased in recent years, the overall assessment put Tehran’s influence far lower than lawmakers such as Mr. Duncan and Mr. McCaul suggest.

No one from the State Department was called to testify at Tuesday’s hearing before the House Subcommittee on Oversight and Management Efficiency. Despite Mr. Nisman’s absence, others testifying included Douglas Farah, a former journalist and president of IBI Consultants; Ilan Berman of the American Foreign Policy Council; Blaise Misztal of the Foreign Policy Bipartisan Policy Center; and Joseph Humire of the Center for a Secure Free Society.

Mr. Farah claimed Iran’s influence in Latin America and the Caribbean is “in fact growing on multiple fronts.”

“To understand how,” he said, “one must understand the changing context in which Iran is operating in Latin America, including the bloc of nations allied with Iran and the transnational criminal pipelines that traverse the hemisphere and successfully breach our southern border thousands of times each day.”

Iranian leaders, noted Mr. Farah, have a “doctrine of asymmetrical warfare against the United States and its allies that explicitly endorses as legitimate the use of weapons of mass destruction.”

Others were circumspect.

“With the passing from the stage of Iranian President Mahmoud Ahmadinejad and Venezuelan President Hugo Chavez - the two personalities that, over the course of the last decade, most drove the Iranian-Latin American relationship - Iran’s efforts to secure political backing and economic assistance from Latin America have arrived at a natural inflection point,” said Mr. Misztal.

“Chavez’s death weakened the Venezuelan government and its anti-American allies in Havana, La Paz, and Quito, who form Iran’s natural constituency in the region,” he said. “Their anemic economic performance will further weaken these regimes, and limit their ability to assist Iran.”