Egyptian army helicopters have fired missiles on suspected Islamist militants in Sinai peninsula, security officials say.
Twenty people were reported killed in Touma village, while the Sheikh Zuwaid area to the west was also hit.
The strikes came after security checkpoints were allegedly attacked by gunmen in the town of al-Arish, leaving a number of people injured.
On Sunday, militants killed 16 Egyptian border guards in the area.
After that attack – the deadliest and most brazen against Egyptian troops in this border region for decades – Israeli forces said they killed some of the militants who broke through into Israel.
There has been a heavy military build-up around al-Arish, correspondents report, and Egypt’s Rafah border crossing to Gaza has been indefinitely closed as security forces hunt the remaining attackers.
Egypt is also reported to have begun sealing off the illicit smuggling tunnels into Gaza.
This is the first time Egypt has fired missiles in Sinai since the 1973 war with Israel, when it attempted to recapture the Sinai peninsula, security officials told Associated Press.
Egyptian military presence in Sinai is limited and requires Israeli approval under the terms of the 1979 peace treaty between the nations which returned Sinai to Egyptian control.
Tensions are very high in the area, where Islamic extremists are said to have gained a foothold in recent months, taking advantage of the security vacuum left after former President Hosni Mubarak was ousted last year.
A Sinai army commander told Reuters news agency the army had received information that there were many militants in Touma.
“We have succeeded in entering Touma, killed 20 terrorists and destroyed three armored cars belonging to terrorists. Operations are still ongoing,” he told Reuters. State television also reported the deaths.
The attacks came hours after three security checkpoints were attacked in the main regional town of al-Arish.
Locals said rounds of gunfire could be heard just before midnight and telephone lines and the Internet were cut off.
At least four people – including police officers and a civilian – were wounded in those attacks.
The Egyptian soldiers killed in Sunday’s attack were buried on Tuesday in a funeral marked by angry calls for vengeance.
Some protesters chanted slogans against the Muslim Brotherhood, and according to witnesses, tried to assault Prime Minister Hisham Qandil.
Both Israeli and Egyptian officials blamed Sunday’s attack on Islamist militants – though Egypt’s Muslim Brotherhood, the group to which President Mohammed Mursi belongs, accused the Israeli spy agency Mossad of being responsible.
Israel rejected that claim as “nonsense”.
On Tuesday, Israel handed Egypt six “completely charred” bodies it says are some of the militants behind Sunday’s attack on the Egyptian soldiers, a medical official in al-Arish told AFP news agency. The bodies have not yet been identified.
Israel signalled its approval of Egypt’s strikes, with senior defence official Amos Gilad telling Israel Radio on Wednesday that Egypt was determined to “impose order in Sinai because that is their responsibility… If they don’t remove and uproot [the threat], it will continue to strike”.
The rising violence in the area is a test of credibility for the government of President Mohammed Mursi, correspondents say.
Although it is clear that Israel has approved the build-up of troops around al-Arish, Israel has historically been reluctant to see a large increase in Egyptian troops close to its border.