By Ahmed Aboulenein and Amina Ismail

CAIRO (Reuters) - Egypt imposed a big security clampdown in its cities on Friday as mass demonstrations called to protest against austerity measures failed to take place.

Riot police and armored vehicles filled the otherwise empty streets of central Cairo, but most people stayed at home.

President Abdel Fattah al-Sisi has urged Egyptians not to protest and warned that there would be no going back on economic reforms, no matter how much pain they might cause.

In a boost for the government, the International Monetary Fund's executive board approved a three-year, $12 billion loan to Egypt aimed at supporting the reforms, and the central bank said it received a first tranche of $2.75 billion.

A little-known group calling itself Movement of the Poor had called for Egyptians to protest on Nov. 11 against deepening austerity measures the government says are required to save the Arab world's most populous nation from financial ruin.

But big protests failed to materialize across the country by 8:30 p.m (1830 GMT). Police dispersed several small gatherings and there were some minor clashes. No one was killed or injured.

"The Egyptian people chose stability and development and rejected any calls against that," state television quoted Prime Minister Sherif Ismail as saying.

The calls to protest began in August, but gained traction on social media last week after Egypt raised fuel prices and floated its currency - a move welcomed by bankers but condemned by ordinary people as the latest blow to their diminishing spending power.

The usually busy Tahrir Square was deserted except for armored vehicles with tear-gas launchers and dozens of riot police. Authorities shut down the Sadat metro station to prevent potential demonstrators reaching the square, which has in the past been a center of political protest.

"I don't think anything will happen but this security presence scares people and ensures nothing does," said Shenouda Ishak, a driver in the Cairo district of Shubra.

"SCARES PEOPLE"

There was a heavy security presence in other areas of Cairo, and other cities including Alexandria, Suez, and Minya.

The protests won little support from prominent activist and opposition groups, though they have been backed by the outlawed Muslim Brotherhood.

But in a country where street politics helped to unseat two presidents within two years, authorities were keen to deter protesters. Dozens of people were detained in recent weeks, accused of inciting unrest.

Protesters camped in Tahrir Square in an 18-day demonstration that ended Hosni Mubarak's 30-year rule in 2011. When Egyptians took to the streets in mid-2013 to end a year of Brotherhood rule, general-turned-president Sisi intervened.

Security sources said police chased dozens of protesters away from Arbaeen Square in Suez, near the place where the first protester was killed in 2011. Protesters on Friday chanted against high prices.

In the coastal province of Beheira, police fired tear gas at protesters who threw rocks back. Security sources said 98 suspected Brotherhood supporters were arrested in three cities in Beheira, 14 in Alexandria, and 10 in Suez.

Muslim Brotherhood activists held a limited protest in the hometown of former President Mohamed Mursi but did not clash with police.

SISI CRUSHED DISSENT

Many ordinary Egyptians and activists believe the heyday of street politics is over. After taking power, Sisi crushed dissent and has applied a protest law so strictly that few dare to come out, despite rising public anger.

State media reported police surrounded the entrances of Cairo and other cities to ensure that members of the Muslim Brotherhood did not enter.

The interior ministry said on Thursday that it confiscated a cache of arms and ammunition hidden in a graveyard and house by the Brotherhood in Fayoum province, southwest of Cairo.

The ministry also said it raided five bomb factories around the country on Wednesday, accusing a militant group of coordinating with the Muslim Brotherhood to attack police checkpoints on the eve of the protests.

Stung by street revolts that have made life worse rather than better, many people said they would stay at home.

Reuters spoke to five activists who all said protests would achieve little and feared violence if they did materialize.

"The revolutionary bloc is reticent to protest. We now know that any street action leads to bloodshed. There is no result we can achieve with this regime," said Malek Adly, a human rights lawyer with the Egyptian Centre for Economic and Social Rights.

Sisi came to power promising economic reform and stability but problems have piled up. With a budget deficit of 12 percent and a looming funding gap, Egypt reached a preliminary deal with the IMF for the $12 billion loan in August this year.

TAX RISES, FOOD PRICES BITE HARD

Yet Egyptians feel hit by tax rises, soaring food price inflation and cuts in state subsidies.

Core inflation is almost at eight-year-highs, over 15 percent, as a foreign exchange shortage and a rise in customs duties bite hard in a country that imports everything from sugar to luxury cars.

Egypt raised electricity prices by 25 to 40 percent and introduced a 13 percent value-added tax in August.

The government has tried to win public support for the austerity measures with a billboard campaign and media blitz and also sought to expand social security schemes to shield the poorest from the effects of the rising prices.

But many Egyptians who would not qualify for such schemes complain they can no longer afford meat, while sugar shortages have driven fears of an impending food crisis.

In his speeches, Sisi has sought to persuade Egyptians that a collective sacrifice is necessary to save the country from financial ruin.

But he also warned that the army could be deployed across the country within six hours in the event of street unrest.

(Additional reporting by Mohamed Abdellah, Omar Fahmy, and Mostafa Hashem; Writing by Ahmed Aboulenein; Editing by Pravin Char)