OAKLAND . (AP) — Five men were in custody Tuesday in connection with the shooting of an undercover police officer in Oakland.

Two of those arrested are suspected gang members on parole, Officer Johnna Watson, a police spokeswoman, told The Associated Press on Tuesday.

More arrests could be made in Monday's shooting, she said.

The veteran plainclothes detective is recuperating after he suffered a gunshot wound in his arm while on a stakeout operation in East Oakland, police Chief Howard Jordan said Tuesday.

A group of "armed and dangerous men" approached the undercover officer's vehicle shortly after 6 p.m. Monday, Jordan said.

The officer was not able to return fire, Jordan added. The chief said that investigators don't know if the gunman knew he was shooting at an officer.

"They intended to assault and injure him," Jordan told reporters at a news conference on Tuesday. "These are very dangerous people who will shoot at other people for no reason."

The wounded officer had been conducting surveillance in the area after a shooting Sunday left a man critically injured. No arrests have been made in that case.

Jordan described the wounded detective as "one of our best." His name hasn't been released.

Monday's shooting prompted a manhunt as the Oakland police SWAT team and officers from surrounding agencies flooded the area and a California Highway Patrol helicopter surveyed the scene by air Monday night.

Police arrested one man late Monday and took four others by midday Tuesday. Several guns have been seized as well. It is unknown whether any of those weapons were involved with the shooting.

Authorities were still in the area Tuesday scouring for more possible suspects, Watson said.

"We're still searching. We have some areas that we want to continue checking," Watson said. "We won't stop."