Myanmar is committing crimes against humanity in its campaign against Muslim insurgents in Rakhine state, Human Rights Watch said on Tuesday, and it called for the U.N. Security Council to impose sanctions and an arms embargo.

A government spokesman rejected the accusation, saying there was no evidence and the government was committed to protecting rights. Myanmar has also rejected U.N. accusations that its forces are engaged in ethnic cleansing against Rohingya Muslims in response to coordinated attacks by Rohingya insurgents on the security forces on Aug. 25.

It says its forces are fighting terrorists responsible for attacking the police and the army, killing civilians and torching villages. The military campaign has sent nearly 440,000 refugees fleeing to Bangladesh, most of them Rohingya. They have accused the security forces and Buddhist vigilantes of trying to drive Rohingya out of Buddhist-majority Myanmar.

“The Burmese military is brutally expelling the Rohingya from northern Rakhine State,” said James Ross, legal and policy director at Human Rights Watch. “The massacres of villagers and mass arson driving people from their homes are all crimes against humanity,” he said.

The International Criminal Court defines crimes against humanity as acts including murder, torture, rape and deportation “when committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack”. Human Rights Watch said its research, supported by analysis of satellite imagery, had found crimes of deportation and forced population transfers, murder and attempted murder, rape and other sexual assault and persecution.

The U.N. Security Council and concerned countries should impose targeted sanctions and an arms embargo, the group said. Government spokesman Zaw Htay rejected the accusation, saying no Myanmar government was ever as committed to the promotion of rights as much as the current one. “Accusations without any strong evidence are dangerous. It makes it difficult for the government to handle things,” he told Reuters.