Iran has dismissed a report that raises concerns about its nuclear program as nothing new.

The findings are from the International Atomic Energy Agency , which says it has “credible” information that Tehran has engaged in activities aimed toward developing nuclear weapons — a charge Iran has long denied.

In a report released Tuesday, the IAEA says it has “serious concern” about the information, which it says “indicates” that Iran has worked on a nuclear weapon design, including the “testing of components.”

However, Iran's ambassador to the IAEA says the report is a “historic mistake.” State-run media quotes Ali Asghar Soltanieh as saying the report repeats old charges that Iran has already proved were “fabricated.” He calls the latest findings “unbalanced” and “politically-motivated.”

Some countries remain skeptical of Iran's claims that it has peaceful nuclear intentions.

The United States says the report may lead it to impose additional sanctions against Iran.

Also, U.S. officials said Tuesday that the report shows Iranian scientists have recently worked on high-speed detonators and computer modeling looking at the behavior of nuclear weapons under different conditions. Additionally, they said it showed work on a neutron initiator in 2006. The officials said the only application for such research is “to weaponize.”

On Monday, Germany said it would call for “greater political and diplomatic pressure” on Tehran if the IAEA report confirmed Western suspicions about a military dimension to Iran's nuclear work.

But Russia criticized the IAEA for distributing the report to the agency's 35-nation governing board. In a statement Tuesday, the Russian foreign ministry said the move appeared to be intended to prevent a diplomatic solution to the dispute at a time when there is a chance of renewed talks between Iran and world powers.

The U.N. Security Council has imposed four rounds of sanctions on Iran for failing to suspend sensitive nuclear activities that have both military and peaceful uses.