Reuters –  Tajikistan has issued an international arrest warrant for the commander of its elite police force who joined Islamic State, prosecutors said on Wednesday, accusing him of treason.

Colonel Gulmurod Khalimov, the U.S.-trained head of the Central Asian state's police force known as OMON, disappeared in April.

Last week a video posted online showed him dressed in black, brandishing a sniper rifle and threatening to bring holy war to Russia and the United States.

Khalimov's defection alarmed many in Tajikistan, an impoverished Muslim nation which borders Afghanistan and is still volatile after a 1992-97 civil war that killed tens of thousands.

Countries across post-Soviet Central Asia have stepped up military drills with Russia and the United States, saying they are determined to confront militant Islam.

Khalimov, 40, is wanted for crimes including high treason and illegal participation in military actions abroad, the Tajik Prosecutor General's office said in a statement.

"Acting for mercenary means, he joined the international terrorist organisation calling itself Islamic State", the prosecutors said.

"Khalimov ... is used as an actor ... in a video spectacle aimed to extol this so-called 'Islamic State' and justify its monstrous crimes," they added.

Khalimov appeared in the professionally-made video in front of a palm tree, and sporting a new beard. His location was not clear.

The International Crisis Group think-tank estimates around 4,000 Central Asians are fighting for Islamic State, an ultra-hardline Islamist group that has seized large parts of Syria and neighboring Iraq and launched attacks in Libya.