Iran and the International Atomic Energy Agency have resumed talks, but failed to find common ground over the nuclear watchdog's probe into Tehran's nuclear program.

IAEA Director General Rafael Mariano Grossi and the head of Iran's Atomic Energy Organization, Mohammad Eslami, met on Monday in Vienna.

Grossi said the IAEA is ready to resolve issues quickly through dialogue, and asked Iran to cooperate in the probe into nuclear substances found at undeclared sites in the country between 2019 and 2020.

But Eslami rejected the request, accusing the IAEA of making what he calls a baseless and fabricated allegation.

Consultations between the two sides stalled in June after the IAEA board adopted a resolution criticizing Iran's responses to the discovery.

In a retaliatory measure, Iran removed some of the cameras monitoring its nuclear activities.

The issue has become a sticking point in indirect talks between Iran and the United States to salvage the 2015 nuclear deal aimed at curbing Tehran's nuclear program in return for lifting sanctions.