Iran on Friday rejected allegations by the US director of national intelligence James Clapper that the Islamic republic was more willing now to carry out attacks on American soil.
"Iran categorically denies James Clapper's unfounded allegations," foreign ministry spokesman Ramin Mehmanparast said.
"Those who are themselves accused of supporting the assassination of Iranian scientists in Tehran cannot allow themselves to make such false and inexact allegations," he said.
In written remarks on Tuesday to senators, Clapper said an alleged plot last year to assassinate the Saudi ambassador to the United States showed Tehran might be more willing now to carry out attacks on US soil.
"Iran's willingness to sponsor future attacks in the United States or against our interests abroad probably will be shaped by Tehran's evaluation of the costs it bears for the plot against (Saudi Arabia's) ambassador as well as Iranian leaders' perceptions of US threats against the regime," he said.
The United States made its allegations early last October and claimed it traced the supposed plot back to the Quds Force, a special operations unit of Iran's Revolutionary Guards.
Iran has repeatedly denied any involvement in the plot, which have strained its already frayed relations with Saudi Arabia.
A key US Senate panel on Thursday adopted a sweeping package of tough new sanctions aimed at forcing Iran to freeze its controversial nuclear programme amid escalating worries of a military confrontation.
The Senate Banking Committee approved the harsh new measures by voice vote, without dissent, as part of a mounting campaign in the US Congress to tighten the economic screws on defiant Iran.
Tehran denies Western charges that it seeks the ability to build a nuclear weapon, insisting its atomic activities are an effort to develop a civilian power-production capability.
Mostafa Ahmadi Roshan, a 32-year-old deputy director of Iran's main uranium enrichment plant, was murdered on January 11 along with his driver/bodyguard when assassins on a motorbike fixed a magnetic bomb to their car.
It was the fifth such incident targeting Iranian scientists in the past two years. Four other scientists -- three of them involved in Iran's nuclear programme -- died in the attacks.
Iranian officials say the attacks are a covert campaign by Israel and the United States.