WASHINGTON - The US will today send another Predator drone on patrol flights along its border with Mexico, allowing authorities for the first time to monitor the entire frontier with the unmanned aircraft.
National Guardsmen will also arrive at the border this week as part of the Obama administration's plan to strengthen security and combat smuggling.
With immigration a critical issue in midterm elections in November, the President, Barack Obama, last month signed into law a $US600 million ($674 million) bill aimed at reinforcing border security, including programs aimed at countering the smuggling of drugs and migrants.
His administration is also pressing for a comprehensive immigration reform measure that would probably allow many of the millions of illegal migrants in the US to legalise their status.
Many Republican politicians say no immigration measure can be considered unless the federal government can ensure security along the border to prevent a spillover from Mexico's crime-ridden north and to prevent the arrival of more illegal migrants.
The Secretary of Homeland Security, Janet Napolitano, said the first unmanned aerial system flight from Corpus Christi in Texas would mean the whole border from California to Texas was now covered.
''Unmanned aerial capabilities will now cover the south-west border - from the El Centro sector in California all the way to the Gulf of Mexico in Texas - providing critical aerial surveillance assistance to personnel on the ground,'' she said.
Ms Napolitano said the drone would begin flights today to provide ''critical aerial surveillance assistance to personnel on the ground''.
The US, deeply concerned by the raging drug war in Mexico, has allocated 1200 National Guard soldiers and 1500 new agents to the border. The first National Guardsmen were expected to arrive in Arizona this week. Texas is to receive 250 National Guard personnel, who will perform a support role until additional border patrol agents are hired and trained.
The Governor of Texas, Rick Perry, says the number of National Guard personnel is insufficient to provide adequate security. Mr Perry, a Republican seeking re-election, is asking for 1000 National Guardsmen to be paid for with federal funds and assigned just to Texas.
Ms Napolitano, a former Arizona governor, said that what ''we are seeing today is the most serious approach to border enforcement that I have seen in my career''.
The new border security law includes two additional Predator B unmanned aerial vehicles for the south-west border, which should be operational next year.
Ms Napolitano said those two drones and the one that will begin flying this week would give Customs and Border Protection a fleet of six to monitor the 3200-kilometre border.
San Antonio Express-News, Agence France-Presse