Iran's nuclear chief said Monday that "terrorists and saboteurs" might have infiltrated the International Atomic Energy Agency in an effort to derail his nation's atomic program, in an unprecedentedly harsh attack on the integrity of the U.N. organization and its probe of allegations that Tehran is striving to make nuclear arms.

Fereydoun Abbasi also rebuked the United States in comments to the IAEA's 155-nation general conference, reflecting Iran's determination to continue defying international pressure aimed at curbing its nuclear program and nudging it toward cooperation with the IAEA inspection.

As such, the speech was bound to give a greater voice to hardline Israeli leaders who say that both diplomatic efforts and economic penalties have failed to move Iran, leaving military strikes as the only alternative to stopping it from developing nuclear weapons.

Israeli Prime Minister Benjamin Netanyahu made a direct appeal to American voters on Sunday to elect a president willing to draw a "red line" with Iran.

In the past week, Netanyahu has urged President Barack Obama and other world leaders to state clearly at what point Iran would face a military attack. But Obama and his top aides, who repeatedly say all options remain on the table, have pointed to shared U.S.-Israeli intelligence that suggests Iran hasn't decided yet whether to build a bomb, despite pursuing the technology and that there would be time for action beyond toughened sanctions already in place.

Iran has often warned that any Israeli attack would trigger a devastating response, and on Monday Abbasi suggested that such strikes would not succeed in slowing down his country's nuclear program. He said without elaboration that experts have "devised certain ways through which nuclear facilities remain intact under missile attacks and raids."

Tehran denies seeking nuclear arms, and Abbasi, an Iranian vice president whom the agency suspects may have been involved in nuclear weapons research, again insisted on Monday that his country's nuclear program is aimed only at making reactor fuel and doing medical research.

"The Islamic Republic of Iran ... has always opposed and will always denounce the manufacture and use of weapons of mass destruction," he said.

Tehran has long dismissed suspicions that it may re-engineer its uranium enrichment program from making reactor fuel to produce nuclear warheads and says accusations that it has worked secretly on nuclear arms are based on fabricated U.S. and Israeli intelligence. It also frequently accuses the IAEA of anti-Iran bias in its push to ensure that all of Tehran's nuclear activities are peaceful. But Abbasi's comments Monday were the harshest to date on the agency itself.

"Terrorists and saboteurs might have intruded the agency and might be making decisions covertly," he said. Citing what he said was an example of sabotage last month at an underground enrichment plant, he said IAEA inspectors arrived to inspect it shortly after power lines were blown up.

"Does this visit have any connection to that detonation?" he asked.

It appeared to be the first mention of the alleged sabotage attack. The plant at Fordo, about 70 kilometers (40 miles) south of Tehran, is of particular concern to Israel because it is buried deep into a mountainside to protect it from attack. It also is being used to enrich uranium closer to the level needed for a nuclear warhead than what is used to power reactors.

Abbasi said that anti-Iran elements are helped by the agency, even when it reports what it sees "truthfully and with absolute honesty," because "this information is easily accessible to saboteurs and terrorists through IAEA reports."

However, Iran now can "ward off threats by targeting ... cyber-attacks, industrial sabotage and use of explosives," he said, without elaborating.

Abbasi said U.S. pressure on Iran is the equivalent of an attack on all developing nations' nuclear rights. He called U.S-led sanctions on Iran's oil exports and financial transactions "the ugly face of colonization and modern slavery."

"A state which has used nuclear weapons is not eligible to be present at the Board of Governors," he said, questioning the right of the United States to sit on the 35-nation IAEA board that makes agency policy.

Meanwhile, statements critical of Iran on Monday were voiced in more traditional terms similar to that heard at previous IAEA meetings.

U.S. Energy Secretary Stephen Chu accused Tehran of continuing "a decade-long pattern of evasion regarding questions over the nature of its nuclear program, including those related to possible military dimensions of its nuclear activities."

A European Union statement warned of "deep concerns about possible military dimensions" to Iran's nuclear program.