KABUL - President Hamid Karzai's rival in a November 7 run-off presidential vote demanded on Monday that Afghanistan's chief election official be sacked, laying out a ultimatum that could complicate the pre-election process.

In one of the deadliest days for U.S. troops in years, the NATO-led force said at least seven U.S. soldiers died in a helicopter crash in western Afghanistan and four others in a separate mid-air helicopter collision in the south.

In Kabul, shouting Down with America, Afghans clashed with police protesting against what participants said was the desecration of a copy of the Koran by foreign troops.

The events come in a politically charged period as Afghanistan braces for the run-off after the first round election in August was marred by allegations of widespread fraud.

The poll, pitting Karzai against ex-foreign minister Abdullah Abdullah, is crucial to Western efforts to stabilize Afghanistan at a time when the insurgency is at its strongest since U.S.-led forces ousted the Taliban from power in 2001.

In a move that could fuel tensions further, Abdullah demanded Afghanistan's top election official Azizullah Ludin be sacked and the interior, education and tribal affairs ministers suspended during the election period.

We will wait for the commission's reply until October 31 and until then we suspend all of our relations with the commission, he told reporters in the garden of his house in Kabul. He refused to say what he would do if these condition were not met.

Concerns about a repeat of the fraud that tainted the first round have cast a shadow over election preparations. More than 200 election officials are being sacked or replaced to prevent a repeat of fraud and many suspect polling stations will be closed.

Ali Daoud Najafi, Ludin's deputy, could not immediately say if there was any suggestion that the election chief might be removed but shrugged off Abdullah's statement.

It has no affect on us at all, he told Reuters.

NATO said seven U.S. service members and three U.S. civilians were killed when a helicopter they were aboard crashed in western Afghanistan following an operation against insurgents in which a dozen Taliban fighters were killed.

In a separate incident four U.S. service members were killed and two injured when two helicopters operated by NATO-led troops collided in mid-air in southern Afghanistan.

Although NATO said neither crash was caused by hostile fire, the incidents highlighted the risks foreign troops in Afghanistan face, as U.S. President Barack Obama deliberates whether to send additional troops there.

PROTESTS

Underscoring many Afghans' unease with the presence of foreign troops, hundreds of people gathered in central Kabul on Monday shouting anti-American slogans and throwing stones.

For the second consecutive day, police fired into the air to break up the crowd as protesters prepared to set fire to a crudely made effigy of Obama outside the parliament building.

Protesters say NATO forces burned a copy of Islam's holiest book during a raid in eastern Afghanistan last week.

The NATO-led force in Afghanistan has denied any involvement and blamed the Taliban for spreading false rumors.

Police arrested up to 30 people, a Reuters witness said. At least one police officer was injured in the clashes, another witness said.

Hundreds of people also gathered in the western city of Herat on Monday in related anti-U.S. protests, a Reuters witness said.

Afghanistan has seen protests in the past over similar incidents, as well as over cartoons depicting the Prophet Mohammad in a Danish newspaper in 2006.

Security has been tightened in Kabul ahead of the November 7 vote, particularly after the Taliban vowed to disrupt the poll and urged Afghans to boycott it, as they had done before the August 20 first round election.

(Writing by Maria Golovnina; Additional reporting by Golnar Motevalli; Editing by Sanjeev Miglani)

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