LOS ANGELES (AFP) - A second suspect has been arrested for allegedly opening fire on two Los Angeles police officers, the FBI said on Thursday, with the United States still on edge over the murders of two New York officers.

The alleged shooter James Brooks, 19, was arrested on Wednesday in Las Vegas, the FBI said in a statement.

The authorities launched a manhunt for Brooks, who, with an accomplice, allegedly opened fire on the LA police officers in their patrol car on Sunday, said officials, who added that no one was injured. The other suspect was detained shortly after the incident, the authorities said.

Law enforcement across the United States has been on alert after the fatal shootings of the two officers in New York earlier this month.

America's largest city was left in shock by the killings of Wenjian Liu, 32, and Rafael Ramos, 40, shot in the head as they sat in their patrol car in broad daylight in Brooklyn on Dec 20.

The two officers were slain following nationwide demonstrations over the killing of several black suspects by police, amid historically bad relations between US law enforcement and the African-American community.