By Michael Georgy
CAIRO (Reuters) - Egyptian ground troops and helicopter gunships attacked Islamist militants in the Sinai Peninsula on Friday in their drive to stem a security threat now spilling over into the rest of the country.
Three soldiers were wounded in clashes in three separate villages, security officials said.
Islamist militancy has risen sharply in the relatively lawless region adjoining Israel and the Gaza Strip and elsewhere in Egypt since the army ousted Islamist President Mohamed Mursi on July 3, following mass protests against his rule.
There are rocket and grenade attacks on soldiers and policemen in the Sinai nearly every day, and about 50 have been killed since July. A Sinai-based militant group claimed responsibility for a failed suicide bombing attack on the interior minister in Cairo last week.
Authorities are also focused on Mursi's Muslim Brotherhood, one of the oldest and most resilient Islamist movements in the Middle East, which had held power for over a year when Mursi was ousted.
Thousands of pro-Mursi protesters marched after Friday prayers in the Cairo district of Nasr City after authorities boosted security in areas where large protests had gathered in the past.
Demonstrations were also held in the cities of Fayoum, Alexandria, Assiut and Qena. State television said clashes broke out between Brotherhood supporters and residents of the Nile Delta town of Mahala.
CRACKDOWN ON BROTHERHOOD
Security forces have killed hundreds of Brotherhood supporters and arrested thousands in one of the toughest crackdowns the group has faced in its 85-year history. It denies accusations that it has carried out terrorist acts.
Many Egyptians, disillusioned with Mursi's moves to give himself sweeping powers and his mismanagement of the economy, were relieved when he was removed and then detained.
The general who toppled him and promised a political roadmap that would lead to elections early next year, army chief Abdel Fattah al-Sisi, enjoys widespread popularity. Speculation is growing that he will run for president.
Many Brotherhood members went underground. But some still take part in marches, a risky step in a country where the authorities seem determined to crush the Islamists.
"Down, down with military rule!" shouted the demonstrators in Cairo. Some walked to a military hospital and wrote graffiti on a wall reading: "The coup is terrorism and Sisi is a killer."
The government imposed a national state of emergency for a month on August 14, and on Thursday extended it by two months because of the security situation.
Al Qaeda, which thrives on instability, has taken notice of the political turmoil in Egypt, a strategic U.S. ally.
Al Qaeda leader Ayman al-Zawahri has described the army-installed government's crackdown against the Brotherhood as a "brutal crime" and urged Egyptians to resist what he called a campaign against Islam.
"LONG DRAMA AWAITS"
In an audio speech released a day after the 12th anniversary of al Qaeda's September 11 strikes on the United States, the former doctor condemned last month's violent break-up of protest camps in Cairo, in which hundreds were killed, and the arrests of Islamists.
"This is an episode of a long drama that awaits Egyptians if they don't unite to implement sharia Islamic law and free their country," said Zawahri, himself an Egyptian who was tortured by authorities under ousted strongman Hosni Mubarak.
Zawahri also said the United States was conspiring in Egypt and called on Egyptians to fight the "oppression".
Egypt, the most populous Arab state, put down an insurgency by supporters of Zawahri in the 1990s.
Egyptian state television on Thursday accused the Palestinian Islamist group Hamas, an offshoot of the Brotherhood that rules neighboring Gaza, of training Egyptian Islamists in how to carry out bombings.
That suggested the authorities intended to pile even more pressure on the Brotherhood, which emerged from the shadows to win every election after a popular revolt toppled Mubarak in 2011. In Gaza, Hamas denied the allegations.
The burning question is to what extent militant groups will turn their sights on Cairo, a move that would further hurt an already punch-drunk tourism industry and hammer a reeling economy. In addition to the attack on the interior minister, there have already been several smaller bomb attacks on police in the capital.
Gunmen fired on an army checkpoint in the southern city of Assiut on Friday, wounding two soldiers, the state-run Al-Ahram newspaper said.
(Editing by Kevin Liffey)