Mexican drug cartels have displaced the mafia as the "number one organized crime threat" in the United States, Sen. Joe Lieberman said Monday as his Senate committee heard testimony in Phoenix on border violence. 

Lieberman, an independent Democrat from Connecticut, and Sen. John McCain, a Republican on Lieberman's panel, told FOX News that the United States needs to step up the fight against the drug cartels. The two senators were in Arizona, McCain's home state, to hear from local officials on their advice for dealing with the drug-fueled violence many fear is spilling across the border. 

"This is literally a war," said Lieberman, chairman of the Senate Homeland Security and Governmental Affairs Committee. "They're fighting for the turf." 

Lieberman has said he plans to seek $380 million in additional funding to help law enforcement stop the flow of guns and drugs across the border. On Monday, he praised Mexican President Felipe Calderon's campaign to fight the cartels, but said cartels have already taken root north of the border -- driving a kidnapping surge in Phoenix and operating, he said, in at least 230 U.S. metropolitan areas. 

"The Mexican drug cartels have become the number one organized crime threat in America, displacing the mafia," Lieberman told FOX News. 

McCain said the federal government needs to approve border states' requests for more National Guard troops, something Homeland Security Secretary Janet Napolitano has said is under review. 

"I think we can have significant control of our border," McCain said. "We should heed the governors who are having to fight this ... all the time." 

But Arizona Gov. Jan Brewer said the Department of Defense has effectively denied her request to send 250 additional National Guard troops to the Arizona-Mexico border to help authorities battle immigrant and drug smuggling and related violence. 

The governor told Lieberman's committee meeting Monday that she was disappointed with the denial of her request to bring the number of troops at her state's southern boundary up to 400. One hundred fifty troops are already there as part of a long-standing border assistance program. 

The Bush administration sent thousands of Guard troops to the border to perform support duties so that federal border authorities would be freed up to focus on border security. Bush's buildup began in 2006 and ended last year. 

The Associated Press contributed to this report.