WRAPUP 10-Mousavi seeks to overturn Iran election result

* Biden casts doubt on outcome of vote

* Mousavi formally appeals against election result

* Tens of thousands join Ahmadinejad victory rally

* Ahmadinejad calls vote "clean and healthy" (Adds further clash in Tehran, paragraph 13)

By Parisa Hafezi and Fredrik Dahl

TEHRAN, June 14 (Reuters) - Defeated candidate Mirhossein Mousavi demanded on Sunday that Iran's presidential election be annulled and urged more protests, while tens of thousands of people hailed the victory of the hardline Mahmoud Ahmadinejad.

Mousavi's supporters again took to the streets after violence on Saturday, clashing with police in protests that have underscored political rifts exposed by Friday's disputed vote.

In a statement on his website, Mousavi said he had formally asked the Guardian Council, a legislative body, to cancel the election result. "I urge you, Iranian nation, to continue your nationwide protests in a peaceful and legal way," he added.

The unrest that has rocked Tehran and other cities since results were declared on Saturday is the sharpest expression of discontent against the Islamic Republic's leadership for years.