Islamist militants driving vehicles mounted with machine guns opened fire on a police checkpoint in Egypt's Sinai peninsula on Sunday, killing two policemen and injuring a third in a daring attack, security officials said.

Militants have stepped up their activity in Sinai since last year's uprising, taking advantage of a security vacuum after many members of the hated police force disappeared from the streets. The lawlessness in the Sinai has been complicated by sour relations between the local Bedouin tribes and the security agencies, who were accused of mistreating them under the old regime of Hosni Mubarak.

The policemen opened fire on the attackers, but failed to stop them. The gunmen fled the site, south of the airport in the city of el-Arish, security officials said on condition of anonymity because they were not authorized to talk to the media.

In a separate development, an Egyptian judge referred a police officer to trial after a mobile phone video posted on the Internet purportedly showed him shooting at the eyes of protesters during clashes in November.

Officer Mahmoud Shennawy, dubbed the "eye sniper" by protesters, is charged with attempted murder of five protesters.

The shootings took place during intense clashes between protesters and security officials around Tahrir Square that left more than 40 dead.