Myanmar's military is shelling villages and preventing civilians from getting food and humanitarian help, amid an intensifying crackdown on the rebel Arakan Army in the restive northwestern state of Rakhine that has pushed thousands from their homes, Amnesty International has said.

The human rights group said on Monday its investigations also found that the security forces had used vague and repressive laws to detain civilians in its battle against the Arakan Army, an ethnic Rakhine group that is fighting for more autonomy.

"These latest operations are yet another reminder that the Myanmar military operates without any regard for human rights," Tirana Hassan, Amnesty's director of crisis response, said in a statement. "Shelling inhabited villages and withholding food supplies is unjustifiable under any circumstances."

Fighting between the military and Arakan Army intensified in January after the rebels attacked a police post leaving 13 officers dead.

The military responded by deploying more troops to the region, the site of a massive crackdown on the Rohingya Muslim minority in 2017, in an attempt to "crush" the fighters. The United Nations says some 5,200 people had been forced from their homes on January 28, as a result of the conflict.

There was no immediate response from the Myanmar authorities to Amnesty's report.

Despite the unrest in Rakhine, the Myanmar authorities have made it more difficult for aid groups to work in the region, Amnesty said. On January 10, the Rakhine government barred all UN agencies and international organisations with the exception of the Red Cross and the World Food Programme from operating in the five conflict-affected townships.

"The Myanmar authorities are deliberately playing with the lives and livelihoods of civilians," Hassan said. "As we've seen time and again, the military's priority is not to protect people in the crossfire, but rather to hide their abuses from the international community."

Amnesty said it had also gathered evidence that the military and police were abusing the law to detain and prosecute civilians, including Aung Tun Sein, a Mro village leader who had been picked up in the wake of an outbreak of fighting in the area around his village in mid-January and remained in jail. Ten other men held with him were released.