WRAPUP 12-Ahmadinejad leads Iran vote, challenger defiant

* Official news agency says incumbent Ahmadinejad wins

* Election commission gives him huge early lead

* Challenger Mousavi claims victory despite 'irregularities'

* Voting extended due heavy turnout (Updates vote count)

By Parisa Hafezi and Zahra Hosseinian

TEHRAN, June 12 (Reuters) - State media declared President Mahmoud Ahmadinejad the winner of Iran's election on Friday but challenger Mirhossein Mousavi alleged irregularities and claimed victory for himself.

The state election commission said Ahmadinejad was ahead with almost 69 percent of the votes after 10 million votes -- or 35 percent of all ballot boxes -- were counted. Mousavi had nearly 29 percent.

The official news agency IRNA said: "Dr Ahmadinejad, by winning most votes at the 10th presidential election, has secured his victory."

Mousavi had earlier tried to pre-empt official announcements by calling a news conference at which he alleged there had been irregularities, including a shortage of ballot papers.