KABUL (AP) – A roadside bomb killed four American soldiers in eastern Afghanistan on Sunday – new evidence of rising violence in a region where clashes and attacks in the first two months of 2009 more than doubled from the same period a year ago.

The spike in violence along the border is an early indication that roadside bombs and other ambushes are likely to surge as thousands of new U.S. forces arrive in Afghanistan this year.

A suicide bomber, meanwhile, attacked a NATO convoy in Kabul on Sunday but instead killed two passers-by – among 18 people killed Sunday, officials said.

Clashes and attacks in the eastern province of Kunar surged 131 percent in January and February from the same period in 2008, said Lt. Col. Rumi Nielson-Green, a U.S. spokeswoman.