Iran expressed deepening fury at Israel and the United States on Thursday over the drive-by bombing that killed a nuclear scientist in Tehran the day before, and signaled that its Islamic Revolutionary Guards Corps might carry out revenge assassinations.

News of the scientist’s killing dominated Iran’s state-run news media, which were filled with vitriolic denunciations both of Israel, seen in Iran as the main suspect in his death, and the United States, where top officials have gone out of their way to issue strongly worded denials of responsibility.

Israeli officials, who regard Iran as their country’s main enemy, have not categorically denied any Israeli role in the killing, which came against a backdrop of growing pressure on Iran over its disputed nuclear program. Western nations suspect that Iran is working toward building a nuclear weapon, despite Iran’s repeated assertions that its program is peaceful.

Iran’s official government reaction to the scientist’s killing on Wednesday was more restrained, saying that Iran would not be dissuaded from its right to peaceful nuclear energy and demanding that the United Nations Security Council investigate and condemn the attack. The Iranian ambassador to the United Nations, Mohammad Khazaee, said in a letter to Secretary General Ban Ki-moon that the killing was part of a campaign of terrorist acts against Iran committed by “certain foreign quarters,” an oblique reference to Israel and the United States.