A man tries to extinguish the flames of a burning vehicle during clashes between supporters of Egypt's deposed president Mohamed Mursi and riot police in Cairo January 17, 2014. [Photo/Agencies]

CAIRO - At least four people were killed as clashes between Muslim Brotherhood supporters and police flared up across Egypt on Friday, security sources said.

The violence erupted a day before Egyptian authorities are expected to announce official results of this week's referendum on a new constitution, part of an army-backed transition plan for the Arab world's most populous nation.

One man was killed by a gunshot to the neck in the city of Fayoum, south of Cairo, a local health ministry official said .

Three people were killed in clashes in the Cairo area, the security sources said. Two were shot and the circumstances of the other death were unclear.

Supporters of the Brotherhood also clashed with security forces in the city of Suez, MENA reported, as well as in Ismailia and a number of locations in the capital, security sources said.

In central Sinai, gunmen caused an explosion of a natural gas pipeline supplying an industrial zone. Nobody was hurt but the blast disrupted gas supplies to some factories in the area, security sources said.

Interim Prime Minister Hazem el-Beblawi condemned the attack on the pipeline and vowed to punish such crimes with force.