Two roadside bombs were defused near the U.S. Embassy in the Afghan capital Monday, while security forces foiled a suspected suicide car bombing near a U.S. military base in the country's south, officials said.

The bombs in Kabul were found hidden in a ditch about 300 yards from the heavily guarded embassy compound, said Ehbrar Ahmad, a senior official with a police commando squad.

The car bomb was foiled about a half-mile from Kandahar Airfield, the main U.S. base in southern Afghanistan, said Afghan army commander Gen. Rahmatullah Raufi.

Violence has surged in Afghanistan, with 20 suicide bombings and dozens of roadside bombs in recent months.

A two-day donors' conference for the country begins in London on Tuesday, and authorities fear militants may time high-profile attacks to coincide with the meeting.