A car loaded with explosives and headed for a police station in northern Algeria exploded Tuesday after officers stopped the attack with bullets. At least three people were killed and 23 wounded, the Interior Ministry said.

Officers opened fire on a vehicle that was speeding toward the local police station in the town of Thenia, 40 miles east of Algiers. The vehicle exploded short of the building, leaving a 6.5-foot-wide crater.

The explosion was the latest in a wave of attacks showing that Islamic fighters are regrouping in Algeria, where offensives by security forces and government amnesty offers had thinned the ranks of insurgents in recent years.

Meanwhile, a report Tuesday said police had arrested four people allegedly involved in planning the most serious recent attack: twin homicide bombings Dec. 11 in the Algerian capital that killed at least 37 people, 17 of them U.N. workers.

The four reportedly were preparing a new attack in Algiers, the daily El Watan reported, quoting security sources. Two were scouts who allegedly guided the homicide bombers to their destinations, and two were militants who filmed the bombings, according to the paper, usually reliable on the subject.

The homicide bombings Dec. 11, at U.N. offices and a government building, left little doubt that Al Qaeda in Islamic North Africa, the affiliate of the global terror network that claimed the December attacks, was intent on reviving the insurgency that has wracked Algeria since 1992.

The arrests of the four occurred in Boumerdes, east of Algiers in a region known as a haunt for the Al Qaeda affiliate, El Watan said. Three of the four had no police record.

The paper, quoting security sources, said the arrests provided a partial picture of preparations for the Dec. 11 homicide attacks, including the purchase of the two small trucks at a vehicle market in Tidjelabine. They were loaded with explosive materials in the Boumerdes region at Souk El Had, El Watan reported.

The paper also said a man described as an emir, or leader, of the Algiers area was killed in an ambush near Souk El Had. Police were checking his identity.

No one immediately claimed responsibility for the attempted attack Tuesday in Thenia. The force of the blast stopped a clock on nearby City Hall, setting the time at 6:28 a.m. (0528GMT), and damaged surrounding buildings.

The Interior Ministry said in a statement that two police officers and a civilian were killed. All the 23 wounded were treated at hospitals and released, the ministry said.

The Al Qaeda affiliate said it was behind a similar attack earlier this month in the town of Naciria, east of Algiers. Four people were killed when a vehicle rigged with explosives slammed into the police station there.

The group — which emerged from an alliance between Osama bin Laden's international terrorist network and an Algerian Islamist movement known as the Salafist Group for Call and Combat, or GSPC — increasingly has used homicide bombers to deliver its strikes.

Security has been increasing since the December attacks. The names and photos of 33 alleged Islamists have been hung at police stations. Their ages vary between 24 and 42, and one is a 26-year-old woman from the Algiers region, El Watan said.

Algeria has been battling an Islamic insurgency since 1992. It was triggered when the army canceled the second round of the country's first multiparty elections to prevent a likely victory by a now-banned Muslim fundamentalist party. Up to 200,000 people are estimated to have died in violence since then.