The United States on Monday denied Iranian accusations it assassinated a scientist and urged the Islamic regime not to use the incident to "distract attention" from its contested nuclear program.

Assailants shot dead Dariush Rezaei-Nejad, who was reportedly associated with the defense ministry, and wounded his wife as they waited for their child outside a Tehran kindergarten on Saturday.

Iran's parliament speaker, Ali Larijani, accused the United States and Israel of a "terrorist act."

"We were not involved," State Department spokeswoman Victoria Nuland told reporters in Washington.

"Our sympathies are obviously with the family of the victim. We condemn any assassination or attack on... an innocent person," she said.

"It's frequent practice for Tehran to accuse the West for these kinds of incidents and we hope that Tehran is not planning to use this incident to distract attention from what it needs to do, which is to come back into compliance with international obligations," she said.

The United Nations has imposed four rounds of sanctions against Iran over its refusal to halt uranium enrichment. Western nations accuse Iran of seeking a nuclear bomb, while Tehran insists its nuclear drive is for civilian energy.

Several Iranian nuclear scientists have disappeared in recent years or been targeted in attacks. Iranian media initially said Rezaei-Nejad worked for the Atomic Energy Organization of Iran but on Sunday presented him without explanation as an "electronics master's student."