CAIRO — Egypt showed new toughness Wednesday in confronting militants in the Sinai peninsula, with the military launching overnight airstrikes and President Mohammed Morsi ordering a security shake-up.

The assault marked the first time Egyptian fighter planes have conducted strikes in the region since the end of the country’s war with Israel in 1973. They appear to have been conducted with the blessing of Israel, which has pushed Egypt to aggressively tackle the rise of extremism on its border.

The strikes on Egyptian soil came two days after armed militants in the Sinai killed 16 members of Egypt’s security forces, broke through the border into Israel, and attempted to launch a separate attack there.

Among security officials fired by Morsi on Wednesday were Egypt’s intelligence chief, Murad Mowafi, and the governor of North Sinai Province, Abdel Wahab Mabrouk; the president also ordered his defense minister to relieve the head of the country’s military police, a spokesman said.

The steps signaled a clear, if belated, acknowledgment from Morsi, Egypt’s first Islamist president, that Islamist militants who have taken root in the Sinai posed a significant challenge to Egypt. But they also raised questions about whether Egypt’s US-funded military is capable of addressing the threat from extremists, who advocate self-governance under sharia law.

The use of warplanes by Egypt appeared to show the limitations of a military apparatus whose dependence on tanks and fighter aircraft reflect an orientation more toward land warfare than a counterinsurgency campaign.

‘‘The Egyptian army is well-equipped,’’ said Zeinab Abul-Magd, a history professor at the American University in Cairo and Oberlin College in Ohio who has studied the Egyptian military. ‘‘They have tanks and planes to crush these terror groups. But they have not trained their officers or soldiers to deal with the problems of Sinai.’’

Egyptian state television said Wednesday that overnight bomb strikes, carried out in response to a fresh wave of attacks on checkpoints, had killed at least 20 suspected militants. Sinai residents disputed that account, saying the offensive appeared to have been a show of force and a publicity stunt, and it was unclear if the airstrikes used bombs or missiles.

The deployment of troops and use of force in the Sinai is governed by a US-brokered peace treaty between the two countries that has been in effect since 1979. A senior Israeli official declined to say whether Israel had been asked to sign off on the strikes, but cited ‘‘ongoing contacts’’ between the two countries.

Robert Springboard, an expert on the Egyptian military at the Naval Postgraduate School in California, said the country’s armed forces have never been eager to take on extremist cells in the Sinai. When militant groups carried out bombings in the 1990s and the past decade, Egypt’s intelligence service and Interior Ministry took the lead in the fight against them.

Much of the Sinai has fallen into lawlessness since Egypt’s wintertime revolt in 2011.

For now, Islamic courts are the preferred forum for settling disputes, and security forces seldom stray from the main highway. The area has the potential to become a powder keg, with some jihadists vowing to beat back any attempt by security forces to assert control there.

Morsi is under heavy pressure to endorse a crushing crackdown on militants in the region, but any missteps or abuses could trigger a backlash from Islamists, his main political base.

At the same time, he faces resistance from top generals over the limits of his powers, and it was not clear on Wednesday whether the military had signed off on the ouster of security officials.