* At least 95 killed across Egypt after security crackdown

* Month-long state of emergency imposed across country

* Authorities blame Islamists for provoking violence

* Political, security crisis has divided society (updates death toll)

CAIRO, Aug 14 (Reuters) - At least 95 Egyptians were killed on Wednesday after security forces moved in on protesters demanding the reinstatement of President Mohamed Mursi, and the government imposed a state of emergency as violence swept the most populous Arab nation.

Troops opened fire on Islamist demonstrators in clashes that brought chaos to the capital and other cities and looked certain to further polarise Egypt's 84 million people between those who backed Mursi and the millions who opposed his brief rule.

In the streets around the Rabaa al-Adawiya mosque in northeast Cairo, where thousands of Mursi supporters have staged a sit-in for the last six weeks, riot police wearing gas masks crouched behind armoured vehicles, tear gas hung in the air and burning tyres sent plumes of black smoke into the sky.

Several television stations ran footage of what appeared to be pro-Mursi protesters firing automatic rifles at soldiers from behind sandbag barricades.

At a hospital morgue nearby, a Reuters reporter counted 29 bodies, including that of a 12-year-old boy. Most had died of gunshot wounds to the head.

Violence spread beyond Cairo, with Mursi supporters and security forces clashing in the cities of Alexandria, Minya, Assiut, Fayoum and Suez and in Buhayra and Beni Suef provinces.

The health ministry put the overall death toll at 95 people, including both police and civilians, with other sources saying at least 17 were killed in Fayoum province and five in Suez.

Mursi supporters besieged and set fire to government buildings and several churches were attacked, state media said.

Mohamed El-Beltagi, a leader of Mursi's Muslim Brotherhood movement that has led the protests, said his 17-year-old daughter had been killed in the clashes.

He warned of wider conflict, and singled out the head of the armed forces who deposed Mursi on July 3 following mass protests calling for his resignation.

"I swear by God that if you stay in your homes, Abdel Fattah al-Sisi will embroil this country so that it becomes Syria. Abdel Fattah al-Sisi will push this nation to a civil war so that he escapes the gallows."

By 1400 GMT, only a few hundred protesters remained at the Rabaa site. A second, smaller camp near Cairo University was swiftly cleared in the early morning.

State of emergency

The presidency announced a month-long state of emergency across Egypt and ordered the armed forces to help police enforce security. Rights activists said the move would give legal cover for the army to make arrests.

The interim cabinet, installed by the military to guide Egypt to fresh elections in around six months, also announced a curfew from 7 p.m. to 6 a.m. in several provinces as well as Cairo and Alexandria.

Hosni Mubarak, the U.S.-backed autocratic ruler toppled in a 2011 uprising, imposed a state of emergency after Islamists assassinated Anwar Sadat in 1981 and used it over the next 30 years to stifle dissent and crack down on the Brotherhood.

Lifting the state of emergency had been a key demand of the protesters who ousted Mubarak, and the military eventually did so last year.

The West, notably the United States which gives the Egyptian military $1.3 billion each year, has been alarmed by the recent violence in the strategic Arab ally that has a peace treaty with Israel and controls the vital Suez Canal waterway.

Wednesday's assault prompted widespread condemnation. Turkey urged the U.N. Security Council and Arab League to act quickly to stop a "massacre" in Egypt, and Iran warned of the risk of civil war.

Nine hours after the start of Wednesday's operation, crowds of protesters were still blocking roads, chanting and waving flags as security forces sought to prevent them from regrouping.

"At 7 a.m. they came. Helicopters from the top and bulldozers from below. They smashed through our walls. Police and soldiers, they fired tear gas at children," said teacher Saleh Abdulaziz, 39, clutching a bleeding wound on his head.

"They continued to fire at protesters even when we begged them to stop."

The move to break up the camps appeared to dash any remaining hopes of bringing the Brotherhood back into the political mainstream, and underlined the impression many Egyptians share that the military is tightening its grip.

The operation also suggested the army had lost patience with persistent protests that were crippling parts of the capital and slowing the political process.

It was the third time since Mursi's ouster six weeks ago that security forces had opened fire on protesters in Cairo, killing dozens of people on each occasion.

The crackdown began just after dawn with helicopters hovering over the camps. Gunfire rang out as protesters, among them women and children, fled Rabaa. Armoured vehicles moved in beside bulldozers which began clearing tents.

Markets nervous

The government issued a statement saying security forces had showed the "utmost degree of self-restraint", reflected in low casualties compared to the number of people "and the volume of weapons and violence directed against the security forces".

It added that it would press ahead with implementing an army-backed political transition plan in "a way that strives not to exclude any party from participation".

Mursi became Egypt's first freely elected leader in June 2012, but failed to tackle deep economic malaise and worried many Egyptians with apparent efforts to tighten Islamist rule.

Liberals and young Egyptians staged huge rallies demanding that he resign, and the army said it removed him in response to the will of the people.

Since he was deposed, Gulf Arab states pledged $12 billion in aid to Egypt, buying the interim government valuable time to try to put the country's finances back in order.

Egyptian stocks have rallied 23 percent since his ouster, but fell 1.7 percent on Wednesday. While the drop was relatively muted, market participants are becoming more nervous.

Emad Mostaque, emerging markets strategist at Noah Capital Markets, switched to a "sell" position from neutral on Egyptian equities.

"The organised nature of the Muslim Brotherhood and their chunky presence in society (let's say 10 percent), means they can be far more disruptive than the 2011 revolutionaries," he said in a client note.