Invasion U.S.A.

The film begins by showing a group of Cuban refugees on a boat sailing for the United States. They are at first met by what appears to be a U.S. Coast Guard boat, with armed personnel. The captain of the vessel declares that the refugees are welcomed to the United States, only to have the Guardsmen open fire on them and take several bags of cocaine hidden in the boat. It is revealed that the armed personnel were communist Latin American guerrillas disguised as U.S. Coast Guardsmen.
The real Coast Guard eventually finds the boat full of the murdered Cubans off the coast of Florida. The FBI and the Miami Police Department arrive at the docks to investigate the murders. The communist guerrillas eventually land in Florida and exchange the drugs for weaponry from a drug dealer. They are led by Soviet operative Mikhail Rostov (Richard Lynch), who earlier had been disguised as the fake Coast Guard captain who opened fire on the Cuban refugees. Former CIA agent Matt Hunter (Norris) is asked to come out of retirement, but he declines. When Rostov and a team of guerillas destroy Hunter's residence in the Everglades in a failed assassination attempt, this convinces Hunter to reconsider.
Later in the day, hundreds of additional guerrillas land on the beaches of southern Florida and move inland using several pre-positioned trucks. The guerrillas begin their assault by destroying suburban homes. Another group of guerrillas (impersonating Miami police officers) attack a community center full of Cuban expatriates in Miami. When a squad car with genuine Miami policemen drives by to investigate the gunfire, the survivors angrily start vandalizing their car, leaving the police perplexed. Meanwhile, the FBI has no idea who is behind the attacks. Hunter and the CIA believe that Rostov is behind the attacks. As terrorist acts continue in Miami, race riots and general chaos develop within the city, as the terrorists had planned.
Later that night, the guerrillas start a shootout and bomb threat at a mall where people are doing their Christmas shopping. During the attack, Hunter comes into the mall and takes down the guerrillas one by one. Hunter tracks down the whole group that attacked the mall. National Guard troops are called up, while martial law is declared and armed civilians organize to protect their communities from further guerilla attacks. Hunter continues to go after the terrorists, stopping their plans to bomb a church, killing Rostov's right-hand man Nikko (Alexander Zale) outside of a shop, and saving a school bus full of children. Despite thwarting these attacks, Hunter is discouraged to come to a carnival bombed by the terrorists, realizing that there are too many of them spread out too far for him to effectively stem the overall tide of their attacks.
Alarmed by the threat, the government establishes a special theater command for the southeastern United States with the headquarters in Atlanta, Georgia. At the command center, all 50 state governors and military officials meet to stop the terror attacks. The FBI takes Hunter into custody so he can give his account of thwarting Nikko's attack and he is taken to the command center, where he goads Rostov on national television to come out and kill him. Rostov orders all the guerrillas to assault the center. However, the guerrillas find no one inside the center and the National Guard surrounds the area with tanks and troops, using the arrest of Hunter as a trap. As the battle rages outside, Hunter comes face-to-face with Rostov and finally kills him with a M72 LAW. The terror crisis ends when the remaining guerrillas on the street surrender to the National Guard.

Question: Who does Hunter and the CIA believe is behind the attacks?
Answer: Rostov