ABUJA (Reuters) - Hundreds of people demonstrated outside the headquarters of Nigeria's electoral commission on Wednesday to demand the removal of its chairman ahead of nationwide elections due by next April.

Members of labour unions rallied to demand the removal of Independent National Election Commission (INEC) chairman Maurice Iwu, whom they deem responsible for flawed 2007 polls which brought President Umaru Yar'Adua to power.

Acting President Goodluck Jonathan, who assumed executive powers almost two months ago with Yar'Adua too sick to govern, has made overhauling the electoral system a top priority and reform legislation is before parliament.

But INEC's critics say the reforms will be toothless unless Iwu himself is replaced with someone more credible who can better organise the next polls, due by April 2011.

"Even the president said the (2007) election was flawed. Iwu is the chairman of INEC and he is responsible," Justice Obi, a 33-year-old businessman among the protesters, told Reuters.

"If he stays, rigging will be outrageous, and there is no chance of free elections next year. Forget it," he said.

Behind him demonstrators held up banners with the words "Iwu must go", "A vote stolen is a future hijacked" and "Half-baked electoral reform is poisonous". The protesters planned to march to the National Assembly as police looked on.

Jonathan has moved quickly to assert his authority since assuming presidential powers, removing close Yar'Adua allies including the national security adviser and former justice minister, and last month dissolving the entire cabinet.

Political analysts expect more public officials to be sacked once Jonathan has formed his new cabinet and local media have speculated that Iwu may be among them.

The 2007 polls were so marred by ballot-stuffing and voter intimidation that local and international observers said they were not credible.

Legal challenges to Yar'Adua's victory lasted for months after he took office, undermining his authority for much of the first half of his rule.