Mostafa Ahmadi Roshan with his son. Roshan is the fifth Iranian nuclear scientist whose murder is being linked to Israel.

The New York Times reports: As arguments flare in Israel and the United States about a possible military strike to set back Iran’s nuclear program, an accelerating covert campaign of assassinations, bombings, cyberattacks and defections appears intended to make that debate irrelevant, according to current and former American officials and specialists on Iran.

The campaign, which experts believe is being carried out mainly by Israel, apparently claimed its latest victim on Wednesday when a bomb killed a 32-year-old nuclear scientist in Tehran’s morning rush hour.

The scientist, Mostafa Ahmadi Roshan, was a department supervisor at the Natanz uranium enrichment plant, a participant in what Western leaders believe is Iran’s halting but determined progress toward a nuclear weapon. He was at least the fifth scientist with nuclear connections to be killed since 2007; a sixth scientist, Fereydoon Abbasi, survived a 2010 attack and was put in charge of Iran’s Atomic Energy Organization.

Iranian officials immediately blamed both Israel and the United States for the latest death, which came less than two months after a suspicious explosion at an Iranian missile base that killed a top general and 16 other people. While American officials deny a role in lethal activities, the United States is believed to engage in other covert efforts against the Iranian nuclear program.

The assassination drew an unusually strong condemnation from the White House and the State Department, which disavowed any American complicity. The statements by the United States appeared to reflect serious concern about the growing number of lethal attacks, which some experts believe could backfire by undercutting future negotiations and prompting Iran to redouble what the West suspects is a quest for a nuclear capacity.

“The United States had absolutely nothing to do with this,” said Tommy Vietor, a spokesman for the National Security Council. Secretary of State Hillary Rodham Clinton appeared to expand the denial beyond Wednesday’s killing, “categorically” denying “any United States involvement in any kind of act of violence inside Iran.”