Thousands of Iranian mourners chanted anti-American and anti-Israel slogans on Friday, during the funeral of Mostafa Ahmadi Roshan, the Iranian scientist who was assassinated earlier this week.

The Associated Press reported that the mourners were chanting “Death to Israel” and “Death to America” during the funeral. State TV showed thousands of people carrying Roshan’s coffin through central Tehran, AP reported, before it was taken to a north cemetery for burial. As it marched, the crowd chanted “death to terrorists.”

Iran’s Supreme Leader Ayatollah Ali Khamenei called Roshan’s killing a “cowardly assassination” and accused the U.S. and Israel of being behind the attack.

Roshan, a chemistry expert and a director of the Natanz uranium enrichment facility in central Iran, was killed on Wednesday when two assailants on a motorcycle attached a magnetic bomb to his car in Tehran.

U.S. Secretary of State Hillary Clinton denied any American role in the slaying earlier this week, saying during a press conference, “I want to categorically deny any United States involvement in any kind of act of violence inside Iran.”

U.S. Defense Secretary Leon Panetta also denied any U.S. involvement in the killing, but said Thursday U.S. officials had “some ideas” as to who was behind it.

Iran, meanwhile, has already blamed Israel for the assassination. A website identified with President Mahmoud Ahmadinejad said on Thursday that Iran is preparing its own answers to the string of assassinations of Iranian scientists, adding those responsible had better start staying awake at night.

This report was strengthened on Friday by another report in the independent news website irannuc.ir, which quoted an unidentified security official as saying Iran is preparing a covert counteroffensive against the West in retaliation for the bomb blast. It suggested the retaliation could include assassinations abroad.

“Iran’s intelligence community is in a very good position to design tit-for-tat operations to retaliate for assassinations carried out by Western intelligence services,” the official said, adding: “Iran’s response will be extraterritorial and extra-regional. It follows the strategy that none of those who ordered or carried out (the attacks) should feel secure in any part of the world.”

(Arutz Sheva’s North American Desk is keeping you updated until the start of Shabbat in New York. The time posted automatically on all Arutz Sheva articles, however, is Israeli time.)