Rick Perry
© Reuters / Larry DowningTexas Governor Rick Perry
Texas Gov. Rick Perry sounded the alarm on Thursday over the "very real possibility" that terrorists associated with the Islamic State and other extremist groups have already snuck into the United States via its border with Mexico.

In a speech to the Heritage Foundation in Washington, DC, the former presidential candidate - and potential 2016 contender - said that quick action needs to be taken in order to prevent terrorists from entering the US. Since border security is already lax, he argued, "individuals from ISIS or other terrorist states" could already be within the country's borders.

Perry acknowledged that there is "no clear evidence" that terrorists are in the US, but continued to stress the issue.

"I think there's obvious, great concern about the border not being secure and us not knowing who is penetrating across," he said, as quoted by ThinkProgress. "The cartels, as vicious and brutal as they are, might be the least of our worries. What other bad actors are coming here, or for that matter, have arrived already? Where did they come from? What did they bring with them?"

According to the New York Times, Perry portrayed the situation at the border - in which tens of thousands of undocumented immigrants have illegally entered the US since last October - as a national security issue. He called on the government to not only add more law enforcement officials to keep an eye on the border, but to also deploy drones to the region as a way to implement more effective monitoring.

In a 2013 terrorism assessment, however, the State Department found, "There are no known international terrorist organizations operating in Mexico, and there is no evidence that any terrorist group has targeted U.S. citizens in Mexican territory." It also said no known terror cells related to Al-Qaeda or Hezbollah were operating in the Western hemisphere.

In addition to calling for enhanced border security, the governor threw his support behind a stronger military campaign in Iraq, where the self-proclaimed Islamic State has made rapid territorial gains over the last few months.

"When they talk about limited airstrikes, they place a great emphasis on the word 'limited,' yet clearly more airstrikes are necessary," he said, according to CNN. "Nothing less than a sustained air campaign to degrade and destroy ISIS forces is required."

While Perry was speaking on border and national security issues, he is also battling a grand jury indictment. He is accused of abusing his power by carrying out a veto threat to withhold funding for Texas' anti-corruption watchdog group, but has insisted he acted legally and within his constitutional authority.