KABUL — Roadside bombs killed eight U.S. troops in southern Afghanistan on Tuesday in a pair of attacks that made October the deadliest month for Americans in the 8-year-old war and foreshadowed more violence in the days before a presidential runoff election.
The attacks came a day after 14 Americans died in two helicopter crashes and brought the total number of U.S. service members killed during the month to at least 53, according to the independent Web site icasualties.org.
They also highlighted the danger to foreign forces from a rapid increase in the use of bombs hidden along Afghanistan's rural roads.
U.S. officials have warned that an increase in insurgent attacks is likely prior to the Nov. 7 runoff elections between incumbent President Hamid Karzai and former Foreign Minister Abdullah Abdullah.
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"They are trying to influence the people of Afghanistan to prevent them from voting," said Col. Wayne Shanks, spokesman for U.S. forces in the country.
There was also a spike in attacks leading up to the first round of voting two months ago; 45 U.S. troops were killed in July, and 51 in August, previously the deadliest months for Americans in the military campaign.
The Aug. 20 election was marred by reports of widespread fraud, which cost Karzai nearly 1 million votes and left him just short of the required 50 percent for an outright win.
The Taliban insurgency claimed responsibility for Tuesday's attacks.
"We don't accept these two candidates," Qari Yousef Ahmadi, a Taliban spokesman, said in a telephone interview. "This election is against Islam and against us."
He said the attacks took place in Zabol province. Shanks did not identify the area, pending notification of next of kin, but other military officials put them in neighboring Kandahar province.
Seven of the Americans were killed in a single incident along with an Afghan civilian working with them, Shanks said. The roadside bombing targeted a U.S. armored vehicle patrol and was followed by a firefight in which an unspecified number of insurgents were killed, he said.
The eighth American was killed in a separate roadside bombing, Shanks said.
The increase in casualties could complicate a decision by President Obama on the way forward in Afghanistan. Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, reportedly has requested up to 40,000 additional troops to pursue insurgents in Taliban strongholds, protect civilians and promote development to build support for the government.
There are about 68,000 American troops already in the country, along with 38,000 from 42 countries serving with the International Security Assistance Force.
"The last couple of days have been a very tough couple of days for everybody involved," Shanks said. But "I think you will see, as we work to make this a safer place, the attacks will come down here."
U.S. forces are finding close to two-thirds of the roadside bombs — commonly referred to as improvised explosive devices, or IEDs — before they detonate, he said.
Improvised bombs in Afghanistan differ from those that have confronted U.S.-led troops in Iraq. At the height of the IED threat in Iraq, insurgents commonly relied on military explosives — old artillery shells turned into roadside bombs.
In Afghanistan, there are fewer caches of old munitions, so militants make homemade explosives. Those explosives are less effective, and insurgents compensate by producing bombs that are very large.
Afghan insurgents have few radio-activated bombs, meaning that, unlike in Iraq, American jammers are of little use in defending against many of the explosives. Instead, militants use long wires or pressure plates to trigger explosions. The pressure plates often are made of wood to avoid discovery by metal detectors.
The number of bombs has increased sharply this year, according to the Pentagon IED office. There were 2,548 attempted attacks in 2007, 3,783 in 2008 and 5,612 in the first nine months of this year.