Libya's interim government has named a former military officer under Moammar Gadhafi as the head of the country's army, while clashes between militias in the capital highlighted ongoing security challenges.

The fighting erupted Tuesday in Tripoli between a local militia and one from the city of Misrata, about 200 kilometers to the east. The two sides used machine guns, rocket-propelled grenades and anti-aircraft guns, killing at least four people.

Militias from across Libya helped liberate Tripoli during the uprising that pushed Mr. Gadhafi from power, but tensions have remained as rival groups compete for influence in the country's new government.

In Washington, State Department spokeswoman Victoria Nuland said the United States is concerned about continued fighting, and wants to see issues resolved in a way that makes all Libyans feel they have a place in the country's future.

The interim leaders on Tuesday named Youssef Mangoush to lead Libya's new army.

He resigned from Mr. Gadhafi's military a decade ago, and fought alongside the former rebels during the uprising before being captured by Gadhafi loyalists. He was later freed when anti-Gadhafi fighters overtook the capital.