CAIRO (Reuters) - The Egyptian army has captured six people it regards as "terrorists" in Sinai after an attack on a police station earlier this week that killed 16 border guards near the border with Israel, a military source told state media on Friday.
Egypt sent hundreds of troops and armored vehicles into North Sinai on Thursday to tackle militants operating near the border in an offensive commanders said had killed up to 20 people they deemed terrorists.
The action, which Cairo says is its biggest military operation in the desert region since its 1973 war with Israel, is seen as crucial to maintaining stable relations between the former foes who signed a peace treaty in 1979.
Israel fears Islamist militants based in the increasingly lawless region could link up with Palestinian jihadis in the neighboring Gaza Strip to launch attacks on the Jewish state - potentially jeopardizing the peace accord.
The military source told state television that six militants had been captured in the border settlement of Sheikh Zuwaid, where on Wednesday Egyptian warplanes fired rockets at suspected militant hideouts.
Separately, an army official told the al-Ahram state newspaper that preparations were underway to raid the mountainous Jebel El Halal region in Central Sinai in order to purge it of "terrorist" elements.
A Reuters witness said several army tanks were heading towards al-Arish on Friday, the main administrative centre in North Sinai. In the past two days, the witness had only seen armored vehicles mounted with machine guns in the region.
A security source in North Sinai told Reuters that seven and not six men had been detained, but that figure could not be immediately corroborated.
He said the detained men had been previously arrested after bombings in resorts along Sinai's southern Red Sea coast between 2004-2006 that killed or wounded hundreds of foreign tourists. They had been jailed for months, he said, but were freed without charges.
However, some Sinai residents have been skeptical about the army's reported crackdown, saying they had seen no sign of anyone being killed in what they described as a "haphazard" operation.
Disorder has been spreading in North Sinai, a region with many guns that is bristling with resentment over neglect by Cairo, since the overthrow of President Hosni Mubarak in February last year in a popular uprising. Mubarak's government had worked closely with Israel to secure the border region.
Newly elected Egyptian President Mohamed Mursi, who took office in June, has promised to restore stability.
He arrived in al-Arish on Friday to assess the security situation, the state news agency said. It was Mursi's second visit this week to the border area following the attack.
Mursi has brushed aside accusations that his background in the Muslim Brotherhood, and ideological affinity with the Islamist Hamas rulers in Gaza, might lead him to take a softer line on militants bent on the destruction of Israel.
Mursi sacked the country's intelligence chief on Wednesday and announced other changes in the security apparatus.
Hundreds of protesters gathered in al-Arish on Friday to denounce the attack on the police station and show support for the army. They demanded that the Camp David accord be modified to allow the Egyptian army full control of the peninsula.
They also called for Egypt's al-Azhar institution, the highest authority in Sunni Islam, to help spread moderate understanding of the religion.
"We hope the army's campaign will achieve its goals," said 43-year-old Mohamed Ahmed. "We haven't felt safe for over two years now and we hear about people with weapons in the mountains. We hope the campaign reaches and eradicates them."
Ismail Haniyeh, head of the Hamas government in Gaza, pledged support on Thursday for Egypt's investigations into the attack, but urged it to reopen a vital border crossing closed since then.
Hamas has ruled out suggestions that Palestinian gunmen took part in the Sinai killings and has criticized Cairo for imposing "collective punishment" on the impoverished Mediterranean coastal enclave by sealing the border.
The Rafah crossing normally sees some 800 people a day leave for Egypt and beyond, and is the only window on the world for the vast majority of Gazans.
However, Egypt opened the Rafah border on Friday to allow the return of pilgrims from Saudi Arabia and those stranded on their way back to Gaza, the state news agency said, citing a high-ranking official, without saying how long it would stay open for.
By 1000 GMT around 200 people had been allowed into Gaza through the border gate, a Sinai security source told Reuters.
Egypt has moved to seal myriad smuggling tunnels connecting Sinai and the Gaza Strip since Sunday's attack. The Egyptian state newspaper al-Ahram said on Friday some 150 tunnels had been destroyed. There are believed to be about 1,000 such tunnels.
"We want this crossing to remain open for goods and for people. When this happens there will be no need for tunnels," senior Hamas official Ahmer Bahar told worshippers at a Gaza mosque on Friday.
"Tunnels were an exceptional measure ... When we have a free trade corridor, this issue will come to an end," he said.
Tunnellers on the Egyptian side said Egyptian forces were not closing tunnels that were previously known to them and used to bring food and construction materials to Gaza.
Israel has welcomed Egypt's offensive while continuing to express worries about the deteriorating situation in Sinai, home to anti-Israel militants, disgruntled Bedouin tribes, gun-runners, drug smugglers and al Qaeda sympathizers.
Israel says Palestinian jihadi groups have been crossing from Gaza into Egypt and exploiting the security vacuum there by teaming up with local militants with the aim of attacking Israel's long border which runs south to the Red Sea.
Tourism in Sinai, especially along its Red Sea coast, has risen in the past decade, but security was tightened after the deadly bombings in 2004-2006 carried out by Islamist militants from the north who infiltrated across its wild mountainous interior.
Reporting by Shaimaa Fayed, Ali Abdelatti and Ahmed Tolba in Cairo, Tamim Elyan and Yusri Mohamed in al-Arish, and Nidal al-Mughrabi in Gaza; Writing by Shaimaa Fayed; Editing by Mark Heinrich and Andrew Osborn