WASHINGTON - Missouri police fired tear gas and smoke bombs late Wednesday at protesters demonstrating over the killing of an unarmed black teen by an officer.CNN and other media reported that police officers in riot gear marched toward the protesters near a burned-out gas station where demonstrators have gathered in the town of Ferguson, a St. Louis suburb.TV footage of the fifth straight day of unrest there showed thick clouds of smoke and protesters scurrying through it in the dark.Police also used sonic devices that make a loud ear-splitting sound to try to disperse the crowd, the St. Louis Post-Dispatch reported.Demonstrators taunted the police. "We're not dogs, so what the hell you've got those whipping sticks for? Because you want to whip us like dogs," one protester said, according to the newspaper.Police separately arrested two journalists reporting on the unrest that has roiled Ferguson since aspiring college student Michael Brown, 18, died Saturday in a police shooting.His death has triggered rioting and stirred comparisons with the February 2012 fatal shooting of unarmed teenager Trayvon Martin in Florida.Wesley Lowery, a Washington Post political reporter, and Ryan Reilly, a Huffington Post reporter, were arrested in a McDonald's restaurant after police entered the restaurant and ordered people to leave, the pair wrote on Twitter.In a series of tweets, Lowery said they were given no explanation for their arrest other than "trespassing" and were not charged with any offenses before being released."I'm emotional, but need to note: Ryan and I are fine. Have seen people in Ferguson hurt by gas/rubber bullets. This wasn't that," Lowery tweeted.Lowery also said the police officers "assaulted" him because the two reporters were not leaving the McDonald's quickly enough.Earlier, police fired several shots at a 19-year-old who pointed a handgun in their direction as they dispersed around 30 people who had gathered near where the rioting had occurred, the St. Louis Post-Dispatch said.The young man was taken to hospital and his name has not been released.In Los Angeles, police shot and killed a black man on Monday during what they called an "investigative stop.""It is unknown if the suspect has any gang affiliations," the Los Angeles Police Department said in a statement. "The suspect was transported to a local hospital, and after lifesaving efforts he succumbed to his injuries."Officials in Ferguson urged demonstrators to remain calm. Mayor James Knowles called for "any groups wishing to assemble in prayer or in protest do so only during daylight."Looters targeted more than a dozen businesses in the St. Louis suburb overnight Sunday after a vigil on the sidewalk where Brown died erupted into clashes with police armed with tear gas, clubs and rubber bullets.On Tuesday, US President Barack Obama appealed for calm after the "heartbreaking" incident, noting that the FBI had opened a civil rights investigation into Brown's death.Witnesses and police have given conflicting versions of how the teenager was shot in broad daylight, two days before he was due to start college.