Rebels fired rockets at a military base in Afghanistan, killing two US service members and wounding eight as they were unloading supplies from a helicopter, in one of the bloodiest assaults against American forces since insurgents ramped up their fighting in March.
The killings Wednesday came a day after the country's government warned that Taliban and al-Qaeda fighters had launched a campaign of violence to undermine legislative elections set for September.
US war planes and helicopters rushed to the area around the base in Shkin, 7km from the border with Pakistan, to hunt for the attackers, but found no trace of them, US spokesman Jerry O'Hara said.
The wounded were flown to US-led coalition bases for treatment, he said.
An initial military statement said mortars had hit the base, but O'Hara later said an investigation had found the attackers had fired four rockets.
"This was a serious attack against coalition forces," O'Hara said. "Security is not as good as it should be. But when you look at it over the course of months, incidents are on the decline. But that doesn't appear to be the case today."
He said the victims were part of a mission along the border "preventing foreign fighters from entering into this country to derail the peace process."
Militants based in tribal regions on the Pakistani side of the mountainous border often cross into Afghanistan to launch attacks, according to Afghan officials. Seventeen suspected Taliban rebels were captured in the border area Monday.
The name of the dead service members and the branch of the military they worked for were withheld until their families were notified.
The deaths brought to 148 the number of US service members killed in and around Afghanistan since "Operation Enduring Freedom" began in 2001, according to Pentagon figures.
Wednesday's killings came five days after two other US forces were killed and another wounded when a bomb exploded near a military convoy, also in eastern Afghanistan near the border.
Even though US officials remain upbeat about progress toward peace, there has been a steep rise in bombings, shootings and other killings since spring's warmer weather melted thick snow on mountain passes the rebels use.
Over 800 Iraqi civilians have been killed since the swearing-in of the new Iraqi government.
US and Iraqi forces have hit back hard, killing more than 200 suspected rebels since March, according to US and Afghan officials.
A spokesman for President Hamid Karzai, Jawed Ludin, claimed Tuesday that al-Qaeda and Taliban rebels launched a violent campaign last week to subvert Sept. 18 legislative elections -- the next key step toward democracy three years after US-led forces ousted the Taliban for harboring Osama bin Laden.
Meanwhile, the Afghan government reported Wednesday that negotiations to free a kidnapped Italian aid worker were "close to a conclusion."
Clementina Cantoni, who works for CARE International, was abducted by armed men on May 16 as she was being driven to her home in the capital, Kabul.
"The negotiations are ongoing ... we are close to a conclusion. We are very optimistic," Interior Ministry spokesman Latfullah Mashal told reporters.