Islamic State (IS) militants have destroyed a nearly 2,000-year-old arch in the ancient city of Palmyra, Syrian activists said.

The Arch of Triumph is the latest victim in the group's campaign to destroy historic sites across the territory it controls in Iraq and Syria.

It was one of the most recognisable sites in Palmyra, the central city affectionately known by Syrians as the "Bride of the Desert," which IS seized in May.

The monumental arch sat on top of the famed colonnaded streets of the ancient city, which linked the Roman Empire to Persia and the East.

The Britain-based Syrian Observatory for Human Rights said the IS group blew up the arch but left the colonnades in place.

Palmyra's sprawling Roman-era complex, which also includes remains of temples to local gods and goddesses, has been under attack from IS.

In recent weeks, IS militants blew up two famed temples in Palmyra.