Egyptian warplanes killed 25 Islamist militants in North Sinai on Saturday, security sources said, as the Egyptian president visited the province after a major escalation of the conflict there.

The sources said the airstrikes hit militant targets near the town of Sheikh Zuweid, destroying weapons and explosives caches.

They also said security forces had found about half a tonne of explosives in a tunnel on the border between the Sinai and Gaza.

Egyptian President Abdel Fattah al-Sisi inspected soldiers and police in El-Arish, the provincial capital, on Saturday, the presidency said in statement.

Sisi, dressed in military garb for the first time since becoming president just over a year ago, told troops at least 200 militants had been killed in the fighting in recent days, but added: "For me to say that things are under control is not enough, things are totally stable.

"I tell Egyptians ... the size of forces here (in Sinai) is one percent of Egypt's army."

Militants launched a coordinated assault on military checkpoints in North Sinai on Wednesday, leading to day-long fighting which left more than 100 militants and 17 soldiers dead, the army said.

Egyptian air strikes killed 23 Islamist militants the next day, security sources said.

North Sinai is the epicenter of an insurgency in which an Islamic State-affiliated group called Sinai Province is most active. The Sinai Peninsula borders the Gaza Strip, Israel and the Suez Canal.

The insurgency, aimed at toppling the Cairo government, has intensified since the army ousted Islamist president Mohamed Mursi after mass protests against his rule in 2013.

Government officials have accused Mursi's Muslim Brotherhood of being linked to the recent Sinai attacks and a Cairo bomb that killed Egypt's top public prosecutor on Monday. The Brotherhood denies any involvement in violence.

"There is a clear coordination and synchronization in all of the attacks recently carried out between the Brotherhood and its allies and affiliates," the Foreign Ministry said in a statement on Saturday.

On Friday, Sinai Province said in a statement posted on Twitter by supporters it had launched three Grad rockets towards "occupied Palestine". Reuters could not immediately verify the authenticity of the statements.

An Israeli military source said the rockets landed in Israel without causing any casualties and had been fired from Sinai.

(Reporting by Yousri Mohamed in Ismailia, Omar Fahmy in Cairo; Writing by Shadi Bushra; Editing by Yara Bayoumy and Andrew Roche)