Mexican police have discovered what they believed to be a tunnel used to traffic drugs under the border with the U.S.

Video footage shows federal police officers climbing down into the 33ft tunnel in Nogales - a city divided by the US-Mexico border.

The Mexican side of Nogales is located in the north-western state of Sonora, and its northern side is in Arizona.

Drug traffickers regularly try to build tunnels between the two halves of the city to thwart border controls and this is the third tunnel to be found in the last month.

A Mexican police spokesman urged residents to confidentially report any suspicious activity they saw which could be linked to tunnel-building.

'As part of our service to give security to the border area, federal police officers found a tunnel almost 10 metres long, believed to be used to commit crime,' he said.

Tunnel: Mexican police found the 33ft long tunnel in Nogales - a city divided by the US-Mexico border, with half of the town in Arizona, US, and the other half in Sonora, Mexico

Underground route: Police said they believe drugs as well as migrants may have been smuggled through the 33ft tunnel

Police believe the tunnel may have been used to smuggle migrants as well as drugs into the US from Mexico.

The US Drug Enforcement Administration (DEA) says at least 250 drug tunnels have been built connecting the Mexican state of Sonora with the US state of Arizona - most of them in the Nogales area - since 1990.

It refers to the criminals who use the illicit underground passageways - which often connect to the combined sewage system which runs underneath the border - as 'tunnel rats'.