CAIRO, Sept 2 (Aswat Masriya) - Four "extremists" were killed and six others were arrested in a security crackdown in North Sinai's cities of Rafah and Sheikh Zuweid on Tuesday.

The security campaign was launched in retaliation for an attack on a security convoy in North Sinai, which left 11 conscripts dead earlier on Tuesday, security sources said.

Interior Ministry spokesman Hany Abdel Latif told Aswat Masriya that a landmine exploded on the Rafah-Sheikh Zuweid road.

"Extremists dug a tunnel into the road and planted an explosive device inside it," Azazi told Aswat Masriya. He added that the "extremists" dug a hole in the road to stop the passing vehicles. "When the police vehicle stopped in front of the hole, the extremists remotely detonated the explosive device."

The vehicle was carrying two officers and 11 conscripts, Azazi said.

Police forces and unidentified assailants engaged in crossfire following the explosion, reported state run news agency MENA. Those killed included one officer and ten conscripts.

Two more security personnel were injured in the attack, according to a security source in the North Sinai Security Headquarters.

Egypt's security forces have intensified their security measures in North Sinai in reaction to repeated militant attacks that target army and police officials, which rose significantly since the military ouster of former President Mohamed Mursi last year.

A fact-sheet prepared by Egypt's ministry of foreign affairs put the death toll for terrorism acts which took place since January 2011 and until April 2014 at 971, including 664 security personnel.