BEIRUT – The head of Syria’s military police said in video footage aired by the al-Arabiya network late Tuesday that he has defected and joined the rebel forces battling the government of President Bashar Assad.

Maj. Gen. Abdul-Aziz Jassem al-Shallal is one of the highest-ranking officers to leave the Syrian military, and his defection appeared to signal growing disillusionment among senior commanders about the outcome of the conflict that has left at least 40,000 Syrians dead.

In recent weeks, the Syrian military has adopted increasingly heavy-handed tactics, including firing Scud missiles at rebel positions — a development that observers say reflects the government’s desperation. Rebel forces have also made a number of notable gains, taking control of more than half a dozen military bases and expanding their arsenal with confiscated weapons.

Shallal’s defection comes a little more than two weeks after 13 Syrian military officers crossed into Turkey on Dec. 7.

The spokesman for the Syrian Foreign Ministry, Jihad Makdissi, also left the country in early December under circumstances that the government characterized as a leave of absence but that opposition activists said was a defection.

In the video, Shallal is wearing his military uniform and appears calm, saying he had left the military because of “the diversion of the army from its basic mission of protecting the country to become gangs of murder and destruction.”

In a phone interview with the al-Arabiya satellite network, Shallal said that numerous senior government officials would like to defect but are not able to because of close monitoring by the Syrian security forces.

“Many figures of high rank in the government want to defect, but the situation is not allowing them to,” he said.

Getting Shallal out of Syria into Turkey was a complicated and dangerous operation that was planned and coordinated by the Free Syrian Army, a rebel official said. Loay Mokdad, a logistics officer and spokesman with the rebel force, said that the trip took four days and involved the use of motorcycles and horses, as well as a long trek through the mountains along the border between the two countries.