Police have discovered a sophisticated drug smuggling tunnel the length of two football fields running beneath the Arizona border with Mexico, and arrested three suspects.
The tunnel measuring 220 metres linked a building in San Luis, a small town in far western Arizona, to an ice plant in the Mexican border city of San Luis Rio Colorado, the US Drug Enforcement Administration said.
The clandestine passageway descended more than 17m into the ground and measured 2m in height.
It was equipped with lighting and ventilation, and was the first ever discovered in the small border city south of Yuma.
The non-descript, single-storey building in San Luis had been under surveillance since January, after agents noted suspicious comings and goings there.
A vehicle stop traced back to the building yielded 18kg of methamphetamine, the DEA said.
The nationality of the three suspects arrested was not immediately available.
Under pressure from tightened security along the nearly 3200km southern border in recent years, cash-flush Mexican cartels have increasingly resorted to boring tunnels, particularly to Arizona and California, where geological conditions are favourable.
In the past 10 years, 89 cross-border tunnels have been discovered in Arizona and 50 in California, according to DEA figures.
Late Wednesday night, Mexican troops discovered an incomplete tunnel that began in a warehouse in Tijuana and extended 183m towards a warehouse district in San Diego, but did not breach the US side of the border.