GENEVA, July 3 (Reuters) - The United Nations human rights chief on Friday said another human rights catastrophe was unfolding in Sudan, in the city of al-Obeid in North Kordofan, and urged the world to act.

"The signs from al-Obeid are clear and unmistakable: Another human rights catastrophe is unfolding in Sudan, this time in the capital of the strategic state of North Kordofan," the U.N. high commissioner for human rights Volker Turk told delegates in Geneva during an urgent debate at the U.N. human rights council on the situation in the region.

The urgent debate was called by Britain, whose envoy previously warned of the risk of large-scale atrocities following reports that Sudan's paramilitary Rapid Support Forces and ​allies are massing forces around the city of al-Obeid, which could result in an escalation of the conflict.

Turk told delegates that civilians have been subjected to siege-like conditions for 18 months, with shortages of clean water reaching a critical point in al-Obeid amid relentless drone strikes as the Sudanese Armed Forces and the RSF battle for control over areas surrounding the city.

At least 45 civilians were killed and 41 injured in 15 drone strikes in al-Obeid and surrounding areas between June 6-28 recorded by the U.N. human rights office.

(Reporting by Olivia Le Poidevin, Editing by Miranda Murray)