DUBAI, April 6 (Reuters) - Inaction by the UN nuclear watchdog "emboldens aggression" against nuclear facilities such as the Bushehr power plant, Iran's atomic energy chief Mohammad Eslami said on Monday in a letter addressed to the International Atomic Energy Agency's director.

Eslami said Iran's only functioning nuclear power plant had so far been targeted four times, with the most recent attack in its vicinity on April 4 killing a security staff member and injuring others.

He warned that such attacks could risk the release of radioactive material from an operating reactor and could have “irreparable consequences” for people, the environment and neighboring countries.

He described the attacks as a clear breach of international law, and criticized what he called the agency’s "lack of decisive action", saying mere expressions of concern were insufficient and would embolden further attacks.

(Editing by Toby Chopra)