Libyan transitional government forces attacked Muammar Gaddafi's security headquarters in the center of his hometown of Sirte Monday, hoping that once the buildings had been captured the fight for the city would be won.

The protracted battle for Sirte, a showpiece Mediterranean coastal city largely loyal to Gaddafi, has led to concerns the many civilian casualties will breed long-term hostility that will make it very hard for the National Transitional Council to unite the country once the fighting is over.

NTC forces have repeatedly claimed to be on the point of victory in Sirte, only to suffer sudden reversals at the hands of a tenacious enemy fighting for its life, surrounded on three sides and with its back to the sea.

But as night fell on Sunday, pick-up trucks mounted with anti-aircraft guns pounded the white security buildings on a tree-lined square with a fountain in the center while infantry blasted away with AK-47s from behind a high concrete wall, Reuters witnesses said.

One of the pick-up gunners was shot in the face, his gun rotating repeatedly on its axis as he fell dead to the ground.

We are now in the center of Sirte, Col. Salam Al Shalmany told Reuters at the scene. They are in these buildings about half a kilometer from where we are. Once we finish this, it's over. This has gone on too long.

But advances by NTC forces have often proved fragile. Earlier on Sunday, a large group of fighters, approaching Sirte from the west and trying to pin down Gaddafi loyalists against the sea, saw their advance suddenly collapse into a rout under heavy and accurate mortar bombardment.

Their trademark pick-up trucks raced to the rear, some running on flat tires. One man with arm and leg wounds frantically limped away from the carnage as commanders screamed over the radios for their troops to pull back.

Soon seven fighters lay dead in a field hospital while dozens more were being treated for shrapnel wounds.

GADDAFI COUNTER STRIKES

Elsewhere in the city, grown rich on 42 years of Gaddafi largesse, troops and residents still loyal to the former leader launched counter attacks after losing three landmark buildings -- the hospital, the university and the lavish Ouagadougou center, built to host summits of foreign dignitaries.

Despite the counter strikes, the buildings appeared to remain in NTC hands.

But in just one field hospital to the east of the city, doctors said they had received 17 dead and 87 wounded in Sunday's fighting.

NTC chairman Abdel Jalil told a news conference in the capital Tripoli that his men had reached Sirte city center and were combing the town for snipers.

The only other major Gaddafi-held town, Bani Walid, in the desert to the south, was also under siege from no fewer than five sides, he said.

I think and I hope, with the help of God, the liberation of these two towns will be completed by the end of this week. God willing, he said.

The prolonged struggle to capture Sirte and the other few remaining bastions of pro-Gaddafi loyalists has delayed NTC efforts to set up effective government and restart oil production, the lifeblood of the Libyan economy.

Sirte holds symbolic significance because Gaddafi turned it from a fishing village into a second capital. He built opulent villas, hotels and conference halls to house the international summits he liked to stage there.

Thousands of civilians have fled Sirte as fighting has intensified, describing increasingly desperate conditions for those still inside the seafront city. There is no electricity while drinking water and food are running out.

(Additional reporting by Barry Malone in Misrata and Joseph Logan in Tripoli; Writing by Jon Hemming; Editing by Maria Golovnina)

Libya