KABUL — Three NATO troops — two from Estonia and one from the United States — were killed in attacks in southern Afghanistan as fraud charges continued to pour in today from last week's turbulent presidential vote.

The American service member died in an insurgent attack Sunday, the U.S. military said without providing details. Estonia's Defense Ministry said two soldiers were killed after their unit stumbled on a roadside bomb in southern Helmand province.

It was the 37th death for the U.S. military in Afghanistan since the beginning of August, a month that has seen a jump in attacks and violence as the country prepared for its second-ever direct presidential election last week.

Though millions of Afghans went to the polls, turnout was dampened by Taliban threats leading up to the balloting. Those who voted did so amid rocket attacks in the south, a gunbattle in the capital and fighting that trapped people inside stations in the east.

Allegations of fraud and intimidation have streamed in since election day. The independent Electoral Complaints Commission said today it has so far received about 45 complaints that could affect the outcome of the election if proved valid.

The most common was ballot-box stuffing. Both President Hamid Karzai and leading challenger former Foreign Minister Abdullah Abdullah have accused each other of fraud.

The United Nations urged candidates and the Afghan people to wait for fraud charges to be investigated before doubting the legitimacy of the election.

U.S. commanders predicted a deadly summer after President Barack Obama ordered 21,000 more U.S. troops to Afghanistan to turn the tide against a resurgent Taliban and shift the focus in the fight against Islamist extremism from Iraq.