The UN nuclear watchdog said on Thursday its top investigator Olli Heinonen, head of probes into Iran and Syria, will leave his position for personal reasons after nearly 30 years at the Vienna-based agency.

Heinonen, 63, is head of the International Atomic Energy Agency's (IAEA) safeguards department, tasked with verifying nations' nuclear programmes are not being diverted for military use.

"We confirm that Mr Heinonen informed the director general of his intention to resign as of the end of August for personal reasons," IAEA spokeswoman Gill Tudor said.

Heinonen, a Finnish radiochemist, is probably best known for causing a stir in February 2008 with a power-point presentation given to diplomats which indicated links in Iran between projects to process uranium, test explosives and modify a missile cone in a way suitable for a nuclear warhead.

"With my departure, I know that I leave behind a fine team of department colleagues who will continue to provide the strong support to...Mr Amano as well as to my successor," Heinonen wrote in an email to colleagues seen by Reuters. Japanese diplomat Yukiya Amano took over as head of the IAEA in December.

The agency said Heinonen's successor had not yet been decided. – Reuters