ADDIS ABABA, Nov 16 (Reuters) - U.S. envoy Anthony Lake has flown back to Washington after the latest round of mediation between Ethiopia and Eritrea as reports of fresh fighting between the two sides emerged.

Ethiopia accused Eritrea of shelling civilian targets in the contested frontier region of Badme on Monday.

Government spokeswoman Selome Taddesse told Reuters the Eritrean shelling began early on Monday and was ``consistent with its policy of targeting civilians.''

Ethiopia did not return the fire, she said, giving no indication of casualties.

In recent weeks, there have been intermittent reports of shelling from either side around Badme, the territory at the heart of the border dispute which erupted on May 6.

There was also shelling on the front around the contested border town of Zalambessa late last month, which was under Ethiopian administration until it fell to Eritrea on June 3.

Hundreds were killed on three fronts along the 1,000-km (620-mile) frontier before fighting died down with the onset of the rainy season in mid-June.

In the latest round of shuttle diplomacy, U.S. envoy Lake held talks in both Addis Ababa and Asmara before leaving the region for Washington on Sunday.

Lake, a former U.S. national security adviser, expects to return to the region, a U.S. embassy official told Reuters.

There were no word on any results from Lake's mediation.

ADDIS ABABA, Nov 16 (Reuters) - U.S. envoy Anthony Lake left the Ethiopian capital on Sunday to return to Washington, but has not abandoned attempts to resolve the border conflict between Ethiopia and Eritrea, a U.S. embassy official said on Monday.

Lake, a former U.S. national security adviser, met Ethiopian Prime Minister Meles Zenawi in Addis Ababa and Eritrean President Isayas Afewerki in Asmara last week to try to broker peace between the Horn of Africa nations.

An official from the U.S. embassy in Addis Ababa told Reuters that Lake was expected to return to the region, but declined to say when he might do so.

There has been no word on the content of his discussions with the two leaders from the U.S. or government officials from either side.

Lake's regional tour is part of an attempt by the U.S. government and the Organisation of African Unity (OAU) to resolve a conflict that revolves around the placement of a northwestern section of border between the two countries.

Hundreds died in May and June when the dispute erupted into a ground and air war. Since then an uneasy truce has replaced the fighting, with both sides reinforcing border positions.