EL-ARISH, Egypt (AP) -- Egypt deployed helicopter gunships to the Sinai Peninsula on Monday to hunt for the militants who killed 16 soldiers at a checkpoint along the border with Israel, according to security and military officials. Israel meanwhile stepped up pressure on Egypt to clamp down on the lawless border zone.
The officials said two attack helicopters had been sent and more were expected to arrive in the border town of El-Arish as Egyptian security forces prepared to sweep the region, which has experienced a surge of violence since the ouster of Hosni Mubarak's regime last year.
Suspected Islamists attacked the checkpoint on Sunday, killing the soldiers before stealing two of their vehicles and bursting through a security fence into Israel. Israeli officials say the attack was quickly spotted, hit with an airstrike, and at least eight militants were killed.
Egypt and Israel say both Islamist militants from the Sinai and Palestinian allies from the neighboring Gaza Strip are active in the northern Sinai, attacking both Egyptian security forces and staging raids across the border into Israel. This attack was one of the deadliest in years.
The unrest in the Sinai poses a daunting challenge to Egypt's Islamist President Mohammed Morsi, who since coming to office a little more than a month ago has warmed up to Gaza's Hamas rulers. Hamas officials have condemned the killing of the Egyptian soldiers, but Morsi may still come under pressure to back down from plans to end Egypt's cooperation with the Israeli blockade of the Gaza Strip.
He vowed on Sunday night to make the killers pay for their crime and to restore security to Sinai, home to several of the most popular Red Sea resorts in Egypt. On Monday, he declared three days of mourning for the victims, according to state television.
The Sinai border has been largely quiet for most of the three decades since Israel and Egypt signed a peace agreement, although security forces have for years combated a low-level insurgency in El-Arish and nearby areas. The 1979 treaty restricts the number of troops and the type of weapons Egypt can deploy there.
The peninsula has experienced a security vacuum since Mubarak's overthrow in February 2011, and both cross-border and other insurgent attacks have increased. Israel has agreed in the past to Egypt sending reinforcements to bolster its forces there, but the Egyptian officials did not say whether Israel had signed off on the helicopter deployment.
The officials spoke on condition of anonymity because they were not authorized to speak to the media.
Israeli Prime Minister Benjamin Netanyahu on Monday paid an unannounced visit to the site where the militants broke through, praising Israeli security forces for their swift and effective response and expressing regret for the loss of the Egyptian lives.
"Israel and Egypt have a shared interest in maintaining a quiet border," Netanyahu said. "But when talking about the security of Israeli citizens, Israel must and will rely only on itself," he added.
Other Israeli officials gave more details of the attack and their response.
Brig. Gen. Yoav Mordechai told Army Radio that after killing the soldiers, the militants seized a truck and an armored car, then blew up one of the vehicles to punch a hole through a security fence to enter Israel. He said the gunmen were armed with explosive devices, submachine guns and grenades.
He said that Israeli intelligence services had reports of impending infiltration and sent aircraft to strike as the militants broke through. "We were prepared for it, so there was a hit," he said. He said the military "averted a major attack on southern Israel."
In a video clip released by the military, Israeli military chief Lt. Gen. Benny Gantz said the incident was over within 15 minutes on the Israeli side. Defense Minister Ehud Barak told parliament that eight militants were killed by Israeli forces who struck from the air, as well as with tanks and artillery.
The attack was the third cross-border infiltration since Mubarak's overthrow. In one, in August 2011, eight Israelis were killed. Israel is building a fence along the border to block militants as well as illegal African migrants, but also wants Egypt to crack down harder on the border region.
"We hope this will be a fitting wakeup call for the Egyptians to take things in hand on their side more forcefully," Barak told parliament's foreign affairs and defense committee on Monday.
Egypt-Israel relations have always been cool but since Mubarak was overthrown and Islamists rose to power, Israeli officials have expressed concern that ties would further deteriorate. Israel is particularly concerned that Egypt will ease restrictions on entering and leaving the Gaza Strip.
Sunday's attack took place around sunset near the Egyptian border town of Rafah, when the troops at the checkpoint were having the traditional meal at the end of the daily fast during the Muslim holy month of Ramadan.
Immediately after, Egypt shut the Rafah crossing with Gaza, an ominous sign for the Palestinian territory's 1.6 million people. Israel bars Gazans from entering Israel, so the Rafah crossing -- the only exit from the tiny coastal territory not under direct Israeli control -- is their sole gateway to the outside world.
Gaza officials disowned the attack but gave mixed signals over whether residents of the territory may have carried it out.
Gaza's deputy prime minister, Mohammed Awad of the ruling Hamas movement, said militants from the territory were "not involved in this awful crime." But a leading Hamas member, Mohammed Zahar, undercut that denial, telling Al-Jazeera TV that he asked Egypt to provide the names of possible suspects from Gaza so that "we will immediately bring them to justice."
The attack could harm Hamas' efforts to persuade Morsi to ease restrictions at the crossing. Hamas is an offshoot of the Muslim Brotherhood and had hoped that Morsi, a fellow member of the region-wide movement, would be sympathetic to its requests. But he has moved cautiously, in part because of concerns about an influx of militants from Gaza.
Teibel reported from Jerusalem. Associated Press reporters Ibrahim Barzak in Gaza City, Gaza Strip, and Mohammed Daraghmeh in Ramallah, West Bank, contributed to this report.