Thousands of angry demonstrators destroyed the regional headquarters of Egypt's ruling party, demanding government protection from lawlessness after a downtown shootout between Bedouin tribesmen and local residents, police and witnesses said.

Dozens were injured in clashes in this northern Sinai Peninsula town when plainclothed police attacked the El Arish demonstrators with batons, tear gas and metal chains, police and witnesses said. At least 40 people were arrested and two police officers injured in the clashes, police said.

The trouble in El Arish started Saturday evening when scores of masked Bedouins opened fire in a dispute with local El Arish residents, wounding three people and damaging shops and cars, police said.

Thousands of residents then took to the streets demanding better protection from the masked tribesmen.

"It is a state of severe anger and frustration as a result of the security absence in the town. ... We are not asking to be protected from the Bedouins or anybody else, but we are aiming to attract attention to the lawless state in the town," said Amin al-Qassass, a leader with the El Arish branch of the opposition party Al Wafd.

The demonstrators on Sunday pulled down murals of President Hosni Mubarak from the National Democratic Party's building and set furniture and documents on fire, said Hassan Abdullah, another local opposition leader.

Police officials in Cairo confirmed that the NDP building was destroyed and furniture and other items set ablaze. The officials spoke on condition of anonymity because they were not authorized to speak to the media.

The protesters also set fire to the local council building, a few small stores and burned tires in the streets, said the police officials and al-Qassass.

They also demanded the resignation of the Northern Sinai governor and the local police chief, al-Qassass said.

Tension between the townspeople in El Arish, which is home to 120,000 people, and Bedouins who live outside the town in the vast Sinai desert is not uncommon and confrontations between the two occur occasionally.

Some Bedouins outside of El Arish complain they receive little benefit from the region's tourist boom and are struggling financially. Instead some eke out a living smuggling goods and people across the Israeli border.