A tribal leader says Islamic State militants have seized another town in Iraq's western Anbar province, less than a week after capturing the provincial capital, Ramadi.

Sheikh Rafie al-Fahdawi said Friday that the small town of Husseiba fell overnight. He says police and tribal fighters withdrew after running out of ammunition.

Husseiba is about seven kilometers (four miles) east of Ramadi, where IS militants routed Iraqi forces in their most significant advance in nearly a year.

The Iraqi government plans to launch a counteroffensive in Anbar involving Iranian-backed Shiite militias, which have played a key role in rolling back the IS group elsewhere in the country. The presence of the militias could however fuel sectarian tensions in the Sunni province, where anger at the Shiite-led government runs deep.