The attack in Kunar, a province on the border with Pakistan, occurred late Thursday, said military spokeswoman Master Sgt. Cindy Beam. She gave no further details. The condition of the wounded soldier was not immediately clear.
"Two Marines were killed and one wounded Thursday evening northeast of Asadabad," the provincial capital, Beam said.
U.S. troops based in Asadabad, 120 miles east of the capital, Kabul, regularly come under fire from militants. But the attacks with rockets and small-arms rarely cause casualties.
Workers helping organize national elections slated for September have also been targeted with roadside bombs.
The province is one of several across the south and east of the country plagued by stubborn Taliban-led insurgents. The U.S. military says it has killed more than 80 militants in the past month.
Earlier this month, President Bush outlined five new initiatives to help Afghanistan continue to move toward peace and prosperity so that it never again is a "terrorist factory."
"Security is essential to steady progress and growth," Mr. Bush said. "The forces of many nations are working hard with Afghans to find and defeat Taliban remnants and eliminate al Qaeda terrorists."
Mr. Bush said the United States, which in recent months has increased its force in Afghanistan to about 20,000 troops, is helping to build the new Afghan national army and train new Afghan police and border patrol.
Moreover, Mr. Bush said the United States is: helping foster democracy by training newly elected politicians, expanding culture and education exchange programs, pursing bilateral trade and investment; working to print new textbooks and build schools for both boys and girls, and is providing small business grants to women.
Nearly 500 people have died in violence across the country so far this year. Many are victims of the stubborn Taliban-led insurgency. Others have died in factional fighting linked to the country's booming drug trade.
A senior U.S. military official says the coalition stands "firmly behind the decision" to hold elections in Afghanistan in September — despite violence aimed at stopping them.
The military says plans being drawn up by foreign troops, the United Nations and Afghan leaders will encourage voter registration by increasing security. The U.N. says nearly a third of the Afghans eligible to vote are registered.