Egyptian President Abdel Fattah al-Sisi on Monday enacted a decree allowing military trials for civilians suspected of attacking state infrastructure, after a string of deadly strikes on soldiers.

The decree came after Sisi promised a tough response to what he called an "existential threat" to Egypt posed by militants, following an attack Friday on an army checkpoint in the Sinai that killed at least 30 soldiers.

It places state infrastructure including electricity towers, major thoroughfares and bridges under military protection for two years, allowing the army to try anyone suspected of attacking the public facilities.

"Crimes against public institutions, facilities and properties fall under the jurisdiction of the military judiciary," the decree states.

Egypt has witnessed a surge in militant attacks since the army, then led by Sisi, ousted Islamist president Mohamed Morsi from power in July 2013.

Morsi's ouster also unleashed a deadly police crackdown on his supporters that has left hundreds dead and thousands in jail.

The government has cracked down on protests after Morsi's overthrow, passing a law that banned all but police-sanctioned demonstrations.

The military was already empowered with trying civilians for attacks on the army, but Sisi's decree considerably expands its powers by defining state infrastructure as "military facilities".

"The law will remain in effect for two years after its enactment," the decree said.

Sisi's spokesman, Alaa Youssef, told AFP the decree was not meant to target protests but would deal only with "terrorism".

"There is a big difference between attacking public installations and protesting," he said. "They are two different things."

The law, he said, was aimed at "protecting public installations and utilities from terrorist attacks."

A military tribunal sentenced seven militants to death last week for a series of attacks on soldiers and police in Cairo and the Nile Delta.

Other militants who attacked only policemen have been tried before civilian courts.

Rights groups say military trials can carry swift and harsh verdicts.

An end to civilians appearing before military tribunals was a core demand of the revolutionaries who spearheaded a 2011 uprising that overthrew veteran strongman Hosni Mubarak.

Following Mubarak's ouster, thousands of people accused of a range of crimes were tried before military courts during an army-led transition before Morsi's election in mid-2012.

Sisi, who ousted Morsi after millions protested against the Islamist, has pledged to restore stability after years of turmoil that devastated the economy.

Although reviled by the Islamist opposition and some secular dissidents, he enjoys wide backing, especially from domestic media, for taking tough measures to impose law and order.

On Sunday, the manager of state-run radio said it would launch an awareness campaign on the virtues of military trials.

"The campaign aims at clarifying the image of the military judiciary among the public," Ahmed Ibrahim told the official MENA news agency.

"It is distinguished by its speedy resolution of cases that could greatly contribute to eradicating terrorism," he said.