The United Nations High Commissioner for Human Rights has called for Mexico to take urgent action in the northern border city of Nuevo Laredo, where at least 23 people have disappeared since the start of February.

The human rights authority says there are strong indications that a federal security force is responsible. It says a local human rights organization believes there have been at least 40 such disappearances.

In a statement Wednesday, the U.N. office said that it had documented the disappearances of 21 males and two females, including at least five minors.

According to statements to U.N. investigators, the disappearances typically occur at night while the victims are walking along or driving on roads. Sometimes their burned and bullet-riddled vehicles are found on roadsides.