TEHRAN — Iran is ready to “investigate” U.S. charges that its elite Quds Force plotted to kill the Saudi ambassador to Washington, Foreign Minister Ali Akbar Salehi said Monday, while continuing to deny any Iranian involvement.

“We are ready to patiently investigate any issue, even if it is fabricated,” Salehi told the state-run Islamic Republic News Agency. “We also asked America to give us the information related to this scenario,” he said of the U.S. accusations.

Salehi and other Iranian officials nevertheless continued to maintain that Iran had nothing to do with the alleged plot, which has seriously increased tensions with the United States and its regional ally, Saudi Arabia. The request for documents seemed aimed at punching holes in the U.S. allegations, which Iranian officials have dismissed as a “bad Hollywood script.”

U.N. Secretary General Ban Ki-moon said Monday he has referred official Iranian, Saudi and U.S. letters on the case to the Security Council, Reuters news agency reported.

On Sunday, Iran’s Foreign Ministry summoned the Swiss ambassador for the second time in less than a week to complain about the “baseless” accusations, the semiofficial Fars news agency reported. Switzerland represents U.S. interests in Iran.

Iranian officials also demanded consular access to the main suspect in the case, Mansour Arbabsiar, 56, a used-car dealer and dual U.S.-Iranian national who is awaiting a court hearing in New York.

In an indication of increasing diplomatic pressure on Iran, the country’s supreme leader, Ayatollah Ali Khamenei, issued the latest in a series of defiant statements Monday.

“We will not retreat even one step,” he said in a speech in the western city of Paveh, according to his official Web site. “As in the past, we will also not pay any extortion money in the future.” The commanders of the Quds Force, the elite Revolutionary Guard Corps unit accused of instigating the plot, report directly to Khamenei.

The United States has said it wants to increase pressure on Iran and has started lobbying its global allies to intensify already tough sanctions against the Islamic Republic. It is unclear whether other measures also are being prepared, or whether the United States and Saudi Arabia have handed a set of demands to Iran.

Meanwhile, Saudi Arabia’s King Abdullah, 86, was hospitalized Monday in the capital, Riyadh, where he underwent successful back surgery, the official Saudi Press Agency reported.

The target of the alleged assassination plot, Adel al-Jubeir, is Abdullah’s chief foreign policy adviser.