Egypt's prime minister has denounced the killing of four Shiite Muslims by a Sunni mob that included ultraconservative Salafis in a village near Cairo.

A statement by Prime Minister Hesham Kandil's office on Monday said he was closely following the investigation into the incident to ensure that the culprits are punished.

Egypt is an overwhelmingly Sunni Muslim nation with a tiny community of Shiites. About 10 percent of its 90 million people are Christians.

The Sunday attack came a week after a number of Salafi clerics insulted Shiites during a rally attended by Egypt's Islamist President Mohammed Morsi, who listened silently.

One cleric, Mohammed Hassan, called on Morsi "not to open the doors of Egypt" to Shiites, saying that "they never entered a place without corrupting it."