Ireland's highest ranking Garda officer has urged calm after the drive-by shooting of a teenage girl.

Garda Commissioner Martin Callinan vowed his force was working hard towards bringing 16-year-old Melanie McCarthy's killers to justice.

"I'm very pleased with the progress that's being made at the moment," he said.

A shotgun, believed to be the murder weapon, was recovered close to where the getaway car was abandoned in the CityWest area of Dublin, near Brown's Barn restaurant, minutes after the killing.

The teenage victim, also known by the surname McNamara, was blasted in the head in Tallaght on Tuesday night, while sitting in a car with her boyfriend and two others. It is believed one of the young men was the intended target.

Mr Callinan said he offered his condolences to the girl's family, and appealed for people to take a step back and reflect on what had happened.

Praising calls from Traveller community leaders for calm and full cooperation with investigating officers, the commissioner said his views were the same.

"This is a time for reflection, it's a time for calm and more importantly it is a time for the people who have knowledge about the perpetrators of this crime to come forward and assist the gardai and assist the democratic organs of the state," he said.

"We are well capable of dealing with this particular issue but we need to do it in a calm manner and we need to apply the laws of the land."

The Garda chief defended the deployment of armed officers in Tallaght, adding that the force would do all it could to allay public fears. He said: "As always we have to be conscious of what has just happened and we are doing everything that needs to be done from the assessment of the information that is available to us."