Cairo - Egyptian policemen striking for more pay fired into the air on Sunday to disperse riot control forces trying to prevent them from occupying security headquarters in the northern city of Zagazig, the state-run newspaper al-Ahram reported.
Policemen and non-commissioned officers in the city had gathered at the headquarters the previous day demanding the payment of bonuses to which they say they are entitled.
Riot police fired tear gas at the protesters, causing four injuries, but lost control of the situation when the protesting policemen fired "heavily" into the air, the newspaper reported quoting an unnamed security official as saying.
The two police forces are operated separately.
The strikers have won the support of colleagues from a number of other cities, al-Ahram reported.
The newspaper on Saturday quoted a senior security official as saying that the banned Muslim Brotherhood of ousted president Mohammed Morsi was behind the protest.
Two weeks ago hundreds of civil servants protested in Cairo against a new law regulating their conditions of employment.
It was one of the largest demonstrations the capital has seen since November 2013, when military-backed authorities passed a law effectively banning protests without permission from the police.