A hidden cross-border tunnel used to smuggle migrants and contraband between the US and Mexico will be sealed, Mexican border officials have said.

Running between Ciudad Juarez in Mexico and El Paso in Texas, which sit next to each other on either side of the border, the 300m tunnel was concealed in a storm sewer system and only discovered last week - despite official estimates it took at least a year to build.

Investigators are now looking into whether local officials knew of its construction.

Security has been ramped up on both sides of the border ahead of the inauguration of Donald Trump, who has vowed to launch mass deportations of illegal immigrants once in office.

The tunnel had been reinforced with wooden beams to prevent collapses and was equipped with lighting and ventilation.

Such a structure could have taken at least a year to build, army officials said.

The Mexican Attorney General's Office has been tasked with investigating whether local officials had been complicit in the construction of the tunnel, General Jose Lemus, commander of Ciudad Juarez's military garrison, told Mexican media.

The tunnel was discovered on 10 January, after US border patrol agents removed a metal plate covering the entry hole to the tunnel and then alerted their Mexican counterparts to its existence.

The flow of migrants from Mexico in the US has long overshadowed relations between the two neighbours and became a defining issue of the 2024 US presidential election race that culminated in Trump's victory last year.

Raids to detain and deport migrants living in the US without permission could begin as early as Tuesday - the day after Trump officially returns to the White House - according to US media reports.

Under US diplomatic pressure, Mexico has been conducting its largest-ever migrant crackdown, bussing and flying non-Mexican migrants to the country's south, far from the US border.

But Trump campaigned on a promise to seal the US-Mexico border and his threat to impose 25% tariffs was seen as an attempt to force Mexico into doing more to stop undocumented migrants from reaching the southern border of the US.

In response, the recently-elected Mexican President Claudia Sheinbaum has said she will ask the US to take action to stop the flow of weapons being smuggled from the US into Mexico.