UNITED NATIONS (AP) — The U.N. Security Council is urging Myanmar's government to allow international investigators help probe allegations of human rights violations committed against Rohingya Muslims, saying it remains "gravely concerned" at their current plight.

In a letter to Myanmar's leaders obtained Tuesday by The Associated Press, the council noted the government's commitment to investigate all allegations of violence but made clear it wants more than words. It said independent and transparent investigations with the involvement of the international community "would turn this commitment into concrete action and ensure that all perpetrators of human rights violations and abuses are held to account."

The Security Council, which visited Myanmar on April 30 and May 1, also urged the government "to take steps beyond such investigations" to demonstrate its willingness to protect and promote human rights, including cooperating with all U.N. bodies, especially the U.N. High Commissioner for Human Rights.

The Rohingya have long been treated as outsiders in Buddhist-majority Myanmar, even though their families have lived in the country for generations. Nearly all Rohingya have been denied citizenship since 1982, effectively rendering them stateless, and they are denied freedom of movement and other basic rights.

The latest crisis began with attacks by an underground Rohingya insurgent group on Myanmar security personnel last August in northern Rakhine State. Myanmar's military responded with counterinsurgency sweeps and has been accused of widespread rights violations, including rape, murder, torture and the burning of Rohingya homes and villages. The U.N. and U.S. officials have called the military campaign ethnic cleansing.

Thousands of Rohingya are believed to have died and some 700,000 have fled to neighboring Bangladesh but hundreds of thousands remain in Rakhine.

The Security Council urged Myanmar's government to grant U.N. agencies and humanitarian organizations "immediate, safe, and unhindered access to Rakhine State."

It welcomed the government's commitment on May 1 to work with the U.N. and urged full implementation of a memorandum of understanding with the U.N. refugee agency and U.N. Development Program. The council stressed that "only the U.N. has the capacity and expertise to assist and support" the government in dealing "with a crisis of such scale" in Rakhine.

It urged full implementation of recommendations of a commission led by former U.N. Secretary-General Kofi Annan before the August attacks that called for Myanmar to grant citizenship and ensure other rights to the Rohingya. It also urged the government to promote investment and community-directed growth to alleviate poverty in Rakhine.

The Security Council letter, dated May 31, was addressed to Myanmar's U.N. ambassador, Hau Do Suan. It asked him to transmit the letter to State Counselor Aung San Suu Kyi and Senior Gen. Min Aung Hlaing as well as other officials with whom the council during its visit.

"We would be grateful for a reply to this letter within 30 days," the letter said.

The Security Council sent a separate letter to Bangladesh's government praising its "humanity, compassion and support" for the Rohingya refugees, which it said has "saved many thousands of lives."

Council members also expressed gratitude to Bangladesh for its commitment to continue "providing protection and assistance to these refugees ... until conditions in Rakhine State allow for their safe, voluntary and dignified return" to their homes.

In a third letter, the council asked Secretary-General Antonio Guterres "to remain personally engaged on this crisis." It also asked the U.N. to continuing assisting Bangladesh to help the refugees, "especially during the forthcoming monsoon and cyclone seasons," and to offer assistance to Myanmar.