LASHKAR GAH, Afghanistan (Reuters) - A journalist working for Afghan television station Ariana News was killed by a roadside bomb in the southern province of Helmand on Friday, his employer said, adding to a growing toll on media workers in Afghanistan this year.

Witnesses said Nematullah Zaheer had been traveling with other journalists to report on a police operation just outside the provincial capital Lashkar Gah when their vehicle came under fire and police advised them to leave the main road.

Shortly after leaving the road, the vehicle hit an improvised explosive device and Zaheer was killed.

Ariana News confirmed the death in a statement posted on Twitter.

Prior to Nematullah's death, at least 11 journalists had been killed in Afghanistan so far this year, according to the Afghan Journalists Safety Committee, including two working for U.S. broadcaster National Public Radio who were killed in Helmand in June.

The AJSC said 2016 was the deadliest year ever for journalists in Afghanistan, with growing instances of violence and intimidation against media workers by both the Taliban and individuals linked to the government.

(Reporting by Mohammad Stanekzai; Editing by Simon Cameron-Moore)