An illegal immigrant leans on a plaque marking the U.S. boundary with Mexico at the Las Margaritas border crossing in Nogales, Mexico, on July 26, three days before Arizona's controversial immigration law took effect. (Alonso Castillo/Reuters)

U.S. President Barack Obama on Friday signed into law a bill to improve security at his country's border with Mexico.

The $600-million US measure will pay for the hiring of 1,000 new Border Patrol agents and the purchase of new communications gear — including surveillance drones.

Obama made no comment during the signing ceremony. But he issued a statement Thursday after the U.S. Senate passed the bill, saying he's made "securing our southwest border a top priority since I came to office."

But his administration has come under fire from many Republicans for not doing enough to prevent huge of numbers of Mexicans from illegally crossing the border into the U.S. The issue seems likely to play prominently in this fall's mid-term elections.

The controversy over how best to deal with Mexican migrants came to wide public attention earlier this year, when Arizona passed a controversial law that required law enforcement officers to check the immigration status of anyone they reasonably suspect of being an illegal immigrant.

A federal judge later blocked some of the law's most controversial provisions, but it remains a potent symbol for those who want border security dramatically tightened.

On Wednesday, Florida lawmakers introduced their own immigration bill that would require immigrants to carry valid documentation or be jailed for up to 20 days.