"The humanitarian situation in and around Tripoli has deteriorated sharply over the past three weeks," since military strongman Khalifa Haftar launched an offensive on April 4 against forces loyal to the internationally-recognised Government of National Accord (GNA), the ICRC said in a statement.

"More than 30,000 people are said to have fled their homes and are sheltering with relatives or in public buildings," it said, a figure which Libyan authorities and the United Nations say has risen to almost 35,000.

"Tripoli's basic services and infrastructure, such as hospitals and water pumping stations, which have already suffered from violence over the past eight years, are being weakened further," it said, referring to the insecurity in Libya since the 2011 uprising that ousted Moamer Kadhafi.

Youness Rahoui, the head of office in Tripoli for the ICRC, singled out the impact of the violence, which has focused on Tripoli's southern suburbs, on residents of the capital.

"One of our greatest concerns is for civilians living near the frontlines. Densely-populated residential areas are gradually turning into battlefields," Rahoui said.

He also said it was becoming "increasingly dangerous for medical workers to retrieve the wounded, with mounting reports of indiscriminate shelling".

At least 278 people have been killed and more than 1,300 wounded in the clashes, according to the latest casualty toll from the World Health Organization.

Forces loyal to the GNA, which is based in Tripoli, launched a counter-attack last weekend.