A human rights group urged Myanmar's government Monday to back an independent international investigation into alleged abuses by security forces against members of the Muslim Rohingya ethnic minority, including the reported systematic use of sexual violence.

U.S.-based Human Rights Watch said in a statement that soldiers and Border Guard Police took part in rape, gang rape, invasive body searches and sexual assaults while conducting counter-insurgency operations in the western state of Rakhine from October through mid-December. Witnesses said soldiers and police officers targeted Rohingya women and girls as young as 13 in a security operation launched in the northern part of Rakhine state in October last year.

"The sexual violence did not appear to be random or opportunistic but part of a coordinated and systematic attack against Rohingya, in part because of their ethnicity and religion," HRW said in a report. The report -- based on interviews with 18 women and 10 men who fled to neighboring Bangladesh from Maungdaw district -- documented 28 incidents of rape and other sexual assaults between December and January. "Military and police commanders should be held responsible for these crimes if they did not do everything in their power to stop them or punish those involved."

"These horrific attacks on Rohingya women and girls by security forces add a new and brutal chapter to the Burmese military's long and sickening history of sexual violence against women," said Priyanka Motaparthy, the group's senior emergencies researcher. "Military and police commanders should be held responsible for these crimes if they did not do everything in their power to stop them or punish those involved."

Myanmar's military has long been accused of human rights abuses against members of the country's other ethnic minorities, often while conducting counterinsurgency operations. The government has previously denied such allegations but on Monday pledged to investigate the claims. Zaw Htay, a spokesman for the president, told Anadolu Agency that a government-appointed commission was looking into the new allegations.

Myanmar's nationality law, approved in 1982, denies Rohingyas citizenship. According to the law, foreigners cannot become naturalized citizens of Myanmar unless they can prove a close familial connection to the country. In addition to denying them citizenship, Myanmar also denies freedom of travel and access to education, along with systematic persecution by the Buddhist majority.

Rohingyas are not recognized among the 134 official ethnicities in Myanmar because authorities see them as illegal immigrants from neighboring Bangladesh. They are subjected to forced labor, have no land rights and are heavily restricted by the government. They have no permission to leave the camps built for them, no source of income and rely on the World Food Program to survive. The U.N. considers Rohingyas to be one of the most persecuted minorities in the world.