Cairo - Egypt has tightened control of crossings from the Sinai after an Islamist militant group based in the peninsula said it tried to kill the interior minister in Cairo last week, the state news agency reported on Monday.
Ansar Bayt al-Maqdis claimed responsibility on Sunday for the suicide bombing, and promised more attacks in revenge for a crackdown on Egypt's Islamists, raising fears that militant violence in the Sinai could spread across the country.
A day earlier, the Egyptian military launched a major assault on militants in North Sinai, killing or wounding at least 30 people in clashes close to the Palestinian Gaza Strip.
Sporadic violence continued on Monday, when one supporter of the Muslim Brotherhood was killed and 10 people injured in clashes between soldiers and supporters of the group in North Sinai, state television said.
In two separate incidents in central Sinai, three soldiers were injured when gunmen opened fire, according to state news agency Mena, and one soldier was shot dead by gunmen near the Suez canal city of Ismailia, security and medical sources said.
Islamist militancy has risen sharply in the often lawless region adjoining Israel and the Gaza Strip and elsewhere in Egypt since the army deposed Islamist President Mohammed Morsi two months ago, following mass protests against him.
Thursday's daylight attack was the most spectacular so far.
A suicide car bomber blew himself up next to Interior Minister Mohamed Ibrahim's convoy as he left his Cairo home for work in an armoured limousine. The bomber, a passer-by and an unidentified person were killed and more than 20 wounded.
Security officials said they were assessing the threat posed by Ansar Bayt al-Maqdis, said to have 700 to 1 000 members and considered the second largest jihadist group in Sinai after Salafiya Jihadiya, with an estimated following of around 5 000.
Some officials doubt Ansar Bayt al-Maqdis is capable of attacks outside Sinai.
Security officials told Reuters they were especially concerned that the group, whose name means "supporters of Jerusalem", will use stolen government vehicles for car bombs.
Mena said that Ibrahim had decided to boost security surveillance and tighten control of crossings from the Sinai to other Egyptian regions to coincide with a broad security campaign in the peninsula.
Ansar Bayt al-Maqdis counts Grad rockets among its weapons and produces home-made bombs used against Egyptian security forces and soldiers, security sources said. Rocket-propelled grenades are often fired at buildings housing security forces.
Last year the same group claimed responsibility for rocket attacks launched on Israel from Sinai.
It has also claimed at least 10 attacks in the past two years on a gas pipeline linking Egypt, Israel and Jordan.
Sinai's eastern border with Israel and Gaza is a particularly sensitive one, and Israel made its concerns known when jihadist groups expanded into a security vacuum left by the fall of Egypt's veteran autocrat Hosni Mubarak in 2011.
Since the army toppled Mursi, and especially since security forces killed hundreds of supporters of the his Muslim Brotherhood movement when they smashed protest camps in Cairo on 14 August, there have been online calls from radicals to abandon attempts to achieve Islamist rule by democracy, and instead step up violence.
Security concerns are not limited to the Sinai.
A week ago, militants fired rocket-propelled grenades at a ship passing through the Suez Canal on the Sinai's western edge, vital to world trade as well as Egypt's depleted state finances. A video was released linking them to the al-Furqan group.