Insecurity in significant portions of Afghanistan has hindered election preparations and disproportionately affected Afghan women, a report co-authored by the U.N. mission in the country said Sunday.

Militant violence has risen steadily in the past three years, and a record number of U.S. and NATO troops are now in the country to combat it. Afghans will vote for president and provincial councils in a nationwide election Aug. 20, which the Taliban has vowed to disrupt.

Insecurity has already hampered candidates' ability to run for office and for election officials to prepare polling stations, the report said.

Violence has "severely limited freedom of movement and constrained freedom of expression for candidates and supporters, hampering their ability to campaign openly through public gatherings or door-to-door visits," the joint report from the U.N. mission and the Afghan Independent Human Rights Commission said.

"These restrictions have, in turn, created significant limitations on freedom of association and peaceful assembly, and amplified women's difficulties in participating in the electoral process," it said.

Sima Samar, chairwoman of the Afghan Independent Human Rights Commission, said three women provincial council candidates from Kandahar could not even live there because of security threats, and the report noted that only 39 percent of Afghans who registered for the election in 2008 or 2009 are women.

The report said insecurity in "significant" portions of the country would affect the vote. The top U.N. official in the country, Kai Eide, said he could not define what "significant" meant because the situation could change before voting day. The Interior Ministry has said 10 out of 360 Afghan districts are controlled by militants and that one third of the country is considered to be at high risk of violence.

U.S., European and Afghan officials say they expect minor instances of fraud and violence during the election, but that they hope such incidents are kept to a low enough level that the outcome is seen as legitimate. If voters in the violent south and east are kept from the polls, it could lower the number of votes President Hamid Karzai receives, boosting the chances of his top challenger, Abdullah Abdullah.

Violence has marred several campaigns. The U.N. report said nine people have been killed in apparent election-related violence, including four members of Karzai's campaign when a roadside bomb attack hit a campaign vehicle in northern Jawzjan province. Two members of Abdullah's campaign have also been killed in attacks.

In the country's latest violence, a roadside bomb killed a British soldier in southern Afghanistan on Saturday, officials said Sunday. The death raises the number of international troops slain in August to 20.

Thousands of additional British forces and U.S. Marines have been deployed to southern Afghanistan — the Taliban's heartland — in an attempt to shake militant control and enable the presidential poll to take place.

Elsewhere in the south, a roadside bomb exploded against a convoy of security officials in Zabul province, killing three soldiers, said Gen. Sher Mohammad Zazai, an Afghan army commander.