CAIRO — Thousands of low-ranking policemen on strike across Egypt on Thursday refused orders to work and protested what they claim is the politicization of the force in favor of the president’s Muslim Brotherhood party.


The strike, in its fourth day, is a rare show of defiance by policemen against their superiors. It threatens to unravel a security force already weakened by two years of unrest following the ouster of longtime autocrat Hosni Mubarak.


For decades, Egypt’s police aggressively targeted the Brotherhood and other Islamist groups that were once outlawed. Policemen said they now are being forced to confront protesters angry with Mubarak’s successor, President Mohammed Morsi, and his Brotherhood supporters. They also are angry that they can be tried in military courts and complain that current laws do not protect them when they carry out their duties.


The Interior Ministry said in a statement Thursday that it stands at equal distance from all parties, and that the ministry is being objective in its duties.


The ministry, which oversees police in Egypt, relies on low-ranking policemen to protect government buildings, particularly in the face of angry protests in Suez Canal cities and in areas north of Cairo in the Nile Delta region. Hundreds of policemen have been wounded in the past six weeks of unrest in those areas, and several have been killed in the anti-government protests.


In Cairo, dozens of policemen blocked the entrance to one of the city’s main police stations and expressed anger at Morsi’s policies. Others held a sit-in outside Morsi’s house in his hometown of Zagazig, northeast of the capital.


South of the capital, in Assiut and Luxor, policemen protested what they said is new Interior Minister Mohammed Ibrahim’s attempts to use the force to protect the Brotherhood.