Yangon, Myanmar: The UN has urged Myanmar's de facto leader Aung San Suu Kyi to visit the north of Rakhine state, where the army is accused of carrying out a brutal crackdown on the Muslim Rohingya minority.

The Nobel peace prize winner has faced growing international criticism for not stopping the military's campaign, which has pushed more than 20,000 Rohingya over the border to Bangladesh.

Escapees have told AFP shocking stories of mass rape, murder and arson at the hands of security forces, which took control of the area after deadly raids on police posts in October.

Malaysia has accused the army of "genocide", a charge Myanmar officials have vehemently denied. 

Suu Kyi, a veteran democracy activist who came to power in March, has described the situation as "under control" and asked the international community to stop stoking the "fires of resentment".

In a statement released in New York on Thursday, UN special adviser on Myanmar Vijay Nambiar appealed directly to the peace icon to intervene.

"The adoption of a generally defensive rather than proactive approach to providing security to the local population (has) caused frustration locally and disappointment internationally," he said.

"I also appeal to Daw Suu to visit Maungdaw and Buthidaung and reassure the civilian population there that they will be protected," he added, referring to the locked down area in Rakhine. 

On Friday diplomats from the US and several European countries added their urgent calls for access to the region, saying they were "concerned by delays" in resuming aid deliveries.

"Tens of thousands of people who need humanitarian aid, including children with acute malnutrition, have been without it now for nearly two months," the diplomats said in a statement.

The bloodshed presents the biggest challenge to Suu Kyi since her party won Myanmar's first democratic elections in a generation last year.

It has galvanised Muslim nations around the region, with protesters decrying the crackdown as the culmination of years of discrimination and abuse suffered by the stateless Rohingya.

On Sunday Malaysia's Prime Minister Najib Razak taunted Suu Kyi, who the former junta kept under house arrest for almost 20 years, before a crowd of some 5,000 protesters in Kuala Lumpur.

"What's the use of Aung San Suu Kyi having a Nobel prize?" he asked the protesters. 

"The world cannot sit and watch genocide taking place."

Activists say Buddhist-majority Myanmar's stateless Muslim Rohingya minority are among the most persecuted in the world. 

More than 120,000 have been trapped in squalid displacement camps since the last major outbreak of violence erupted in Rakhine in 2012.