UN refugee and development agencies signed an agreement with Myanmar in June that permitted them to operate in northern Rakhine state where hundreds of thousands of Rohingya Muslims were driven from their homes in a brutal army campaign that started almost a year ago.
The agreement was supposed to let the UN help Myanmar create conditions on the ground that would be conducive to a safe and voluntary return for the stateless Rohingya, many of whom are currently languishing in camps in southeast Bangladesh.
So far they have refused to come back without any guarantee of security or basic rights such as citizenship.
The UN agencies said in a joint statement that requests dating back to mid-June for international employees to be allowed to start work in northern Rakhine state remained unanswered.
Though they highlighted some "encouraging" steps, such as visits to the area by UN officials, they said Myanmar needed to provide "effective access."
The UN refugee agency has kept an office in northern Rakhine state throughout the crisis but staff are not able to work in the field freely.
In Myanmar, the Rohingya are widely regarded as illegal immigrants from Bangladesh. Some 700,000 Rohingya have fled to Bangladesh since August last year.