About 300 Customs and Border Protection agents and officers also will be sent to the border region, along with additional helicopters and other surveillance equipment, they said.

"The border is more resourced and more secure than it's ever been but the work continues and the challenge remains," said Alan Bersin, commissioner of the Customs and Border Protection agency.

The Obama administration has pledged to send up to 1,200 National Guard troops to the area for a year and to seek US$600 million for, among other things, 1,000 new border patrol agents and unmanned aerial detection systems.

Violence along the border has been escalating in recent years. Bersin said illegal crossings have begun to fall while seizures of weapons and drugs have risen.

The largest share of the National Guard force -- 524 troops -- will go to Arizona, where state officials have complained bitterly about lack of security.

Legislators in Arizona have passed a strict law to try to crack down on illegal immigrants but the U.S. Justice Department is challenging it on the grounds that immigration is a federal issue.

While welcoming the Obama administration's measures, Arizona Governor Jan Brewer said it did not "appear to be enough or tied to a strategy to comprehensively defeat the increasingly violent drug and alien smuggling cartels" operating in the desert border state.

"We need the implementation of a federal plan to achieve victory over these brutal cartels and the porous nature of our open border," she said.