A spokesman for militias loyal to Libya's UN-brokered government says Islamic State suicide bombers have attacked their positions around the coastal city of Sirte, killing at least one person.

Brig. Gen. Mohammed al-Ghasri says the Sunday attack involved three cars including an ambulance that "infiltrated our siege" and attacked supply lines and medical units. At least one paramedic was killed and a dozen people were wounded.

Al-Ghasri says his forces remain steadfast and aim to take control of the city before the end of the holy month of Ramadan, which began June 6.

He says IS militants have barricaded themselves in the city centre, hoping to draw in their opponents into a protracted street battle.