Egyptian security officials say military helicopters have fired missiles on suspected Islamist militants near the town of al-Arish in the Sinai peninsula.

Up to 20 people are reported to have been killed.

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, 16 Egyptian border guards were killed in the area.

Israeli forces said they later killed at least seven gunmen who broke through into Israel.

Both Israeli and Egyptian officials have blamed Sunday´s attack on Islamist militants.

However, Egypt´s Muslim Brotherhood has accused the Israeli spy agency Mossad of being responsible.

It said the attack was an attempt to undermine the government of Egypt´s Islamist President, Mohammed Mursi.

Israel rejected the claim as "nonsense".

Patrols have been stepped up in the Northern Sinai, and Egypt´s Rafah border crossing to Gaza has been indefinitely closed as security forces hunt the remaining attackers.

The rising violence in the area is a test of credibility for the government of President Mursi, the BBC´s Kevin Connolly says.

Israel wants tighter security in the Sinai, but it does not want that to be achieved with a large increase in numbers of Egyptian troops near its border, our correspondent adds.

Egypt´s military sent extra tanks and troops into the Sinai last year, under terms that had to be agreed with Israel under the 1979 peace treaty between the two countries. (© BBC MMXII 08/08/12)