DUSHANBE (Reuters) - Tajik police killed four relatives of a former elite police force commander who defected to Islamic State two years ago, two security sources told Reuters on Wednesday, during a raid on a house near the Afghan border.

The United States last August offered up to $3 million for information about Colonel Gulmurod Khalimov, whom it trained in counter-terrorism before he joined Islamic State.

Washington has described Khalimov as “a key leader” of Islamic State, which has seized parts of Syria and Iraq and staged or inspired deadly militant attacks around the world.

According to the security sources, police suspected that some of Khalimov’s relatives were also linked to the militant group and were about to cross the border into Afghanistan.

When police raided a house in the Ibrat village in southern Tajikistan late on Tuesday, the suspects resisted and wounded at least one policeman, the sources said. Police killed two of Khalimov’s brothers and two of his nephews, and detained several people.

Tajikistan’s interior ministry confirmed that one of its officers had received a knife wound, but had no further comments.

In April, Tajik security forces detained Khalimov’s eldest son, Bekhruz, 18, who they said had planned to join his father.

Thousands of people from the predominantly Muslim ex-Soviet region of Central Asia have joined Islamic State and several men have been detained this year over a bombing of the metro in Russia’s St Petersburg as well as a truck attack in Stockholm.