Explosions have been heard near the city of Ajdabiya in eastern Libya, where rebels are fighting for control against forces loyal to Colonel Muammar Gaddafi.
RAF Tornado jets attacked Colonel Gaddafi's forces in Ajdabiya on Thursday.
British Foreign Secretary William Hague said it was difficult to use airpower in the city because Colonel Gaddafi's tanks were within the town itself.
The BBC reports the city is strategically important because it commands a coastal highway, linking the east and west of the country.
Military action over Libya to enforce a United Nations 'no-fly' zone, began last Saturday.
Coalition forces are now into their seventh day of military action there.
Twelve countries are now part of the coalition seeking to enforce a UN Security Council resolution passed last week to protect civilians from attack during fighting between rebels and Col Gaddafi's forces.