Bangladesh is accusing Myanmar of failing to tackle the concerns of over 1 million Rohingya Muslims who fled the country and is urging the U.N. Security Council to take action to ensure their safe return home.

Bangladesh's UN ambassador, Masud Bin Momen, said in a letter to the council circulated Tuesday that while his government continues to engage with Myanmar "in good faith" on arrangements to return the Rohingya, "we regret that the necessary conditions for a safe and sustainable return do not exist in Myanmar."

"Nor has Myanmar taken any demonstrable effort to address the concerns of the Rohingyas and the international community," Momen said in the letter.

The Rohingya face official and social discrimination in predominantly Buddhist Myanmar, which denies most of them citizenship and basic rights because they are looked on as immigrants from Bangladesh even though the families of many settled in Myanmar generations ago. Dire conditions led more than 200,000 to flee the country between 2012 and 2015.

The latest crisis began with attacks by Rohingya insurgents on Myanmar security personnel last August 25. The military responded with counterinsurgency sweeps and a scorched-earth campaign against Rohingya villages. It was accused of widespread human rights violations, including rape, murder, torture and the burning of Rohingya homes. Thousands are believed to have died and about 700,000 fled to Bangladesh.

The UN human rights chief, Zeid Ra'ad al-Hussein, has insisted that the possibility of genocide against Rohingya was real and has called for the issue to be referred to the International Criminal Court.

Momen urged the Security Council to adopt a resolution and take "concerted and determined action to address the Rohingya crisis" so the refugees in Bangladesh can return to Myanmar. He accused Myanmar of attempting to play down "the catastrophic scale of the crisis and its grave impact on Bangladesh" by saying the number of people who fled the country can't be higher than a half million.

Momen also called Myanmar's claim that Bangladesh is violating a 1998 demarcation treaty by building bunkers within 150 feet of the border "false and baseless." He said the closest bunker is 654 feet from the border line.

The Security Council is planning to commemorate the one-year anniversary of Myanmar's violent crackdown on the Rohingya at an open meeting Aug. 28 to be addressed by Secretary-General Antonio Guterres, who has called the Rohingya crisis "ethnic cleansing."

British Ambassador Karen Pierce, this month's council president, said the UK wants the meeting to focus on gaining "unconditional access" to Myanmar for the UN refugee and development agencies so they can work with the Myanmar and Bangladesh governments "to make a credible plan to get the refugees back home in safety, dignity and security."

Momen said Bangladesh wants the council to ensure those conditions in Myanmar so the Rohingya can return. He called the framework for cooperation between the U.N. and the Myanmar government "a step in the right direction."

"There is, however, a need for transparency and a demonstration of concrete deliverables so that the Rohingyas can gain the required trust and confidence that, upon returning to their homes in Rakhine State, they will not be subject to further discrimination and violence," Momen said. He also stressed that "it is of the utmost important" that the Rohingyas still in Rakhine "are guaranteed unconditional protection" through the creation of United Nations-administered "safe zones."

Momen said Bangladesh would welcome assistance from the UN to house Rohingya refugees in shelters that can withstand the current monsoon rains, to protect victims of "grave human rights abuses including sexual violence" from traffickers and exploitation, and to provide basic education and skills.