There is still "no question" of an international invasion of Libya, David Cameron has said despite admitting the constraints on ground forces were making the mission more difficult.
Six civilians were reported killed and dozens more injured in the besieged rebel-held town of Misrata as forces loyal to Muammar Gaddafi kept up a barrage of rockets and other fire.
The Prime Minister said the Nato-led air strikes on regime military targets had helped prevent massacres and the taking of Misrata but opposition forces have called for a stronger intervention.
While the United Nations Security Council authorised "all necessary measures" to protect civilians - it specifically ruled out the presence of any occupying force on the ground.
With the two sides mired in a stalemate, Mr Cameron conceded that meant the international allies were not able to "fully determine the outcome".
Allies had to look at "what more can we do to protect civilian life and to stop Gaddafi's war machine unleashing such hell on his own people", he said.
But while rebel forces were receiving help, including body armour and communications equipment, there was no question of going beyond the UN mandate.
"It is because we have said we are not going to invade, we are not going to occupy (that) this is more difficult in many ways because we can't fully determine the outcome with what we have available," the premier told the Murnaghan show on Sky News.
"But we are very clear that we must stick to the terms of the UN Security Council Resolution, we must keep the support of the Arab world."
Pushed as to whether any UK forces could be involved on the ground, he said: "What we've said is there is no question of an invasion or an occupation, this is not about Britain putting boots on the ground, this is not what we are about here."