A clandestine tunnel discovered on the US-Mexico border allowing entry from Ciudad Juarez into the Texan city of El Paso will be sealed by Mexican authorities, an army official said Saturday, adding that its construction was under investigation.

Discovered on January 10 by US and Mexican security agencies, the tunnel measures approximately 300 meters (1,000 feet) in length on the Mexican side and is equipped with lighting, ventilation and is reinforced to prevent collapses.

Hidden in a storm sewer system operating between both cities, its access is about 1.8 meters high and 1.2 meters wide (6 feet high and 4 feet wide), making for easy passage of people or contraband, said General Jose Lemus, commander of Ciudad Juarez’s military garrison, which is guarding the tunnel.

The tunnel’s construction “must have taken a long time… it could have been one or two years,” Lemus told reporters, declining to give details about how long it had been operating as well as its possible builders and operators.

He said the Mexican Attorney General’s Office was responsible for the investigation and would be in charge of determining if there was complicity by the authorities due to the fact that it was built without them noticing.

Lemus also said clues about the tunnel’s existence and location were discussed by human traffickers on social media platforms like TikTok.

Ahead of the US presidential inauguration of Donald Trump on Monday, both sides of the US-Mexico border have reinforced security measures, as the returning Republican has vowed a massive deportation of migrants soon after he takes office.