PHOENIX (Reuters) - U.S. police in Nogales, Arizona, uncovered a drug-smuggling tunnel from Mexico, the latest of more than 20 illicit passageways found under the border there in recent years, authorities said on Thursday.

The U.S. Immigration and Customs Enforcement agency said the 110-foot-long tunnel measured two feet wide by two feet tall, and was shored up with timber.

The passageway ran about five feet below ground from the yard of a house in Nogales, Mexico, to an opening concealed by plants and rocks on an embankment in the Arizona city of the same name.

Smugglers increasingly bore underground to reach U.S. border cities in Arizona and California from Mexico to beat beefed up security along the line.

The tunnel, the latest of 22 illicit passageways found in the Nogales area in the past three years, was likely completed this week. Agents made no arrests, but found 550 pounds of marijuana inside in bundles while securing the tunnel.

Most of the Nogales-area tunnels branch off from a shared drainage system running beneath the streets of the two neighboring cities.

In 2010, a tunnel was also found under the concrete channel of the Rio Grande River between El Paso, Texas, and Ciudad Juarez in Mexico.

(Reporting by Tim Gaynor; Editing by Cynthia Johnston)