The head of the International Atomic Energy Agency has condemned Iran for barring multiple IAEA inspectors from verifying the country's nuclear activities.

IAEA Director General Rafael Grossi said in a statement on Saturday that Iran had informed him of its decision "to withdraw the designation" of several inspectors.

He said the decision means Iran has effectively removed about one third of the core group of experienced IAEA inspectors assigned to the country.

Grossi strongly condemned what he described as a "disproportionate and unprecedented unilateral measure" that affects the planning and conduct of the IAEA's verification activities.

In response, a spokesperson for Iran's foreign ministry said in a statement that Tehran was countering attempts by Britain, Germany, France and the United States to use the IAEA for political purposes.

The four countries had urged Iran to cooperate with the IAEA's probe into traces of nuclear materials detected at undeclared locations. They made the appeal at the IAEA's Board of Governors meeting on Wednesday.

A withdrawal of the inspectors could affect the IAEA's ability to monitor Iran's uranium enrichment activities. Tehran is producing uranium enriched to up to 60 percent purity. That far exceeds the limit of 3.67 percent set in the 2015 nuclear agreement, which Iran signed with six world powers.

Iran has been ramping up its nuclear program since former President Donald Trump withdrew the United States from the deal in 2018.