UPDATE 1-Libyans storm Islamist militia base in Benghazi

(Releads with demonstrators entering militia HQ)

* Libyans march in Benghazi to support democracy

* Islamist militia denies involvement in U.S. envoy's death

* Islamists hold counter-demonstration

BENGHAZI, Libya, Sept 21 (Reuters) - Pro-government

demonstrators stormed the headquarters of the Islamist Ansar

al-Sharia militia in the Libyan city of Benghazi on Friday,

aiming to evict fighters from the site, Reuters witnesses said.

Ansar al-Sharia has been linked to the attack on the U.S.

consulate in Benghazi last week in which the U.S. ambassador to

Libya and three other Americans died. It denies involvement.

Friday's action against the group appeared to be part of a

coordinated sweep of militia headquarters buildings by police,

government troops and activists following a mass public

demonstration against militia units earlier in the day.

Chanting "Libya, Libya", hundreds of demonstrators entered,

pulling down militia flags and torching a vehicle inside the

compound, th e group's main base in Benghazi.

The crowd waved swords and even a meat cleaver, crying "No

more Al Qaeda!" and "The blood we shed for freedom shall not go

in vain!"

"After what happened at the American consulate, the people

of Benghazi had enough of the extremists," said demonstrator

Hassan Ahmed. "They did not give allegiance to the army. So the

people broke in and they fled."

There was no sign of resistance from the militia at the

compound, once the base of forces of former leader Muammar

Gaddafi.

"It looks like they (militia fighters) wanted to defuse the

situation so they fled," Ahmed said.

"This place is like the Bastille. This is where Gaddafi

controlled Libya from, and then Ansar al-Sharia took it over.

This is a turning point for the people of Benghazi."

The demonstrators also took over a compound belonging to the

Abu Slim Brigade, another independent militia, and another

compound belonging to Ansar al-Sharia.

Thousands of Libyans had earlier marched in Benghazi in

support of democracy and against the Islamist militias that

Washington blames for the assault on its consulate. Hundreds of

Ansar al-Sharia supporters held their own protest.

The "Rescue Benghazi day" demonstration called for the

government to disband armed groups that have refused to give up

their weapons since the NATO-backed revolution last year.

"It's obvious that this protest is against the militias. All

of them should join the army or security forces as individuals,

not as groups," medical student Ahmed Sanallah, 27, said.

"Without that there will be no prosperity and no success for the

new Libya."

"DEFEND BENGHAZI"

Although the main demands of the marchers did not mention

the attack on the U.S. consulate, it seems to have provided a

strong impetus for the authorities to rally support behind the

country's weak government.

U.S. ambassador Christopher Stevens was well liked, and many

Libyans condemned the attack on the consulate despite being

angered by the anti-Islamic U.S.-made film that triggered it.

Some protesters' placards in English read: "We demand

justice for Stevens" and "Libya lost a friend".

Others had mixed views.

"I am out today to defend Benghazi. Killing the ambassador

is a completely separate thing," said 26-year-old Amjad Mohammed

Hassan, a network engineer.

"I don't give a damn about the killing of the ambassador

because the Americans offended the Prophet. I am just here for

Benghazi."

Benghazi, 1,000 km (600 miles) from Tripoli across largely

empty desert, is controlled by various armed groups, including

some comprised of Islamists who openly proclaim their hostility

to democratic government and the West.

Some are identified by local people as being among those who

were at the consulate protest last week. U.S. officials have

described the violence as a "terrorist attack".

Abu Al-Qaa, a demonstrator at the Ansar al-Sharia

counter-demonstration on Friday, said Stevens had been

"preparing for the entry of American troops into Libya".

"The will of the Prophet was to expel infidels from Muslim

lands so that Muslims prevail. Terrorizing your enemy is one of

Islam's tenets," he said.

He said he had fought American troops in Iraq where he was

arrested, sent back to Gaddafi's Libya and jailed for three

years. One banner at the Ansar al-Sharia demonstration read:

"Day to rescue Benghazi or day to rescue America?"

(Additional reporting by Omar Al-Mosmary and Ali Shuaib;

Writing by Marie-Louise Gumuchian; Editing by Andrew Roche)