The U.S. government plans to begin a major air and ground initiative at the U.S.-Mexico border to help keep out illegal immigrants, drug smugglers and terrorists, The New York Times reported.

The $10 million plan is expected to include the first use of unmanned aircraft for border patrol, the addition of several hundred agents and the creation of seven tent complexes to detain illegal border crossers.

The remote-controlled aircraft are slated use beginning in June to supplement manned air and ground patrols.

Meanwhile, following last week's deadly train bombings in Spain, the U.S. Department of Homeland Security has issued a bulletin advising state officials, police and transit agencies to consider additional surveillance.

The attacks in Spain did not prompt the United States to raise its terror alert level, which remains at yellow, indicating an "elevated" threat.

Amtrak and transit systems in many large cities increased surveillance of bridges and tunnels following the attack, The Associated Press reported.

However, a Homeland Security official said there was not a specific indication that terrorists were considering attacks on the United States in the near term.