"Due to increased unrest in Libya, a contingent of US forces supporting US Africa Command temporarily relocated from the country in response to security conditions on the ground," it said in a statement.

It did not detail how many military personnel had been withdrawn from Libya.

Forces loyal to Libyan commander Khalifa Haftar were pressing on at the weekend with an offensive on the capital Tripoli, seat of the internationally-recognised Government of National Accord (GNA).

US Africa Command, headquartered in Stuttgart, Germany, said its mission in Libya involves "military support to diplomatic missions, counter-terrorism activities, enhancing partnerships and improving security across the region".

It said it would "continue to monitor conditions on the ground in Libya and assess the feasibility for renewed US military presence as appropriate".

"The security realities on the ground in Libya are growing increasingly complex and unpredictable," said US Marine Corps General Thomas Waldhauser, commander of US Africa Command.

"Even with an adjustment of the force, we will continue to remain agile in support of existing US strategy."

Libya has struggled since the 2011 overthrow of dictator Moamer Kadhafi which left dozens of militia to fill the void and ally with either the GNA or the rival administration in the east backed by Haftar.

In the renewed fighting, forces backing the GNA have launched air strikes on Haftar's self-styled Libyan National Army (LNA) around 50 kilometres (30 miles) south of Tripoli.

Tripoli residents fearing that large-scale fighting could break out have begun stocking up on food and petrol.