BEIRUT — A team of United Nations experts arrived Sunday in Syria to launch a long-delayed investigation of allegations from both sides in the nation’s conflict that chemical weapons have been deployed on the battlefield.

The so-far unverified charges of chemical weapons’ use have become an incendiary component of the larger global debate about the bloody Syrian conflict, now in its third year with no end in sight.

The 20-member U.N. technical team, headed by Ake Sellstrom, a Swedish scientist, arrived in Damascus in a convoy of U.N. vehicles and was whisked inside a five-star hotel under tight security, according to news accounts from the Syrian capital.