Texas Gov. Greg Abbott on Tuesday declared one of the largest Muslim civil rights and advocacy groups in the U.S. a "foreign terrorist organization," under a proclamation he said would allow the state to attempt to shut it down.

He also designated the Council on American-Islamic Relations "a transnational criminal organization" and said it would not be allowed to buy land in the state. The proclamation also included the Muslim Brotherhood.

Neither the CAIR nor the Muslim Brotherhood is designated as a foreign terrorist organization by the U.S. government.

CAIR told Abbott in a letter that his announcement had no basis "in law or fact." The group accused his office of stoking "anti-Muslim hysteria."

"You do not have the authority to unilaterally declare any Americans or American institutions terrorist groups, nor is there any basis to level this smear against our organization," wrote Robert S. McCaw, CAIR’s government affairs director.