At least three people were killed and 17 wounded early on Monday in Egypt's North Sinai province when suspected militants fired rocket-propelled grenades hitting a bus carrying workers employed at a cement factory, security and medical sources said.
They said the bus came under fire in the city of El Arish, which is at the centre of a sharp rise in Islamist militant attacks in the lawless region bordering Israel and the Gaza Strip since Egypt's President Mohamed Morsi was ousted by the military on 3 July.
According to eye witnesses, the attackers shouted "Allahu akbar!" (God is great) after the bus was hit.
However, army spokesperson Colonel Ahmed Ali has said on Monday morning that a nearby police vehicle was the real target of the attack that killed the three workers.
Ali extended his condolences to the families of the victims.
Commenting on Monday's bus attack, Muslim Brotherhood spokesman Gehad El-Haddad said his group believes the incident was "intelligence-related" and aimed at justifying the "coup" that instigated the removal of Morsi.
El-Haddad, who has been in the public eye over the past few weeks due to his intensive comments on Egypt's political scene, also stressed the Brotherhood "unequivocally rejects all types of violence."
Hardline Islamist groups based in North Sinai have intensified attacks on police and soldiers over the past two years, exploiting a security and political vacuum following the 2011 uprising that ousted autocratic president Hosni Mubarak.
Confrontations between militants and Egyptian security forces have further increased since the ouster of Morsi, who hails from the Muslim Brotherhood.
On Friday, a policeman died in a militant attack on a checkpoint in Sinai, which had last week witnessed the killing of at least ten other policemen in different assaults.
Opponents of the Muslim Brotherhood have largely blamed the recurrent clashes in Sinai on the Islamic group.
Many have further linked the Brotherhood with Sinai's militants after Mohamed El-Beltagy, one of the group's leading figures, said in a recent interview the peninsula would see no violence the moment Morsi is reinstated.
Morsi's overthrow was part of the armed forces' roadmap for Egypt's future, which was enforced following mass protests across Egypt against the former elected president.