Myanmar's de facto leader Aung San Suu Kyi on Friday said authorities were looking into allegations of atrocities committed against the Muslim Rohingya minority, as she faces mounting criticism over her handling of the crisis.

Speaking during a trip to Japan, the Nobel Prize winner said the government had "not tried to hide" claims of abuse by the military and pledged a thorough investigation according to the law.

The crisis in northern Rakhine state, where activists and residents say troops have raped villagers, looted towns and torched homes, has posed the biggest challenge to Suu Kyi's government of her six months in power.

"We have not accused any particular organisation or group of engaging in any particular kind of activity because we do not have enough evidence," she told a press conference.

"All this will be made public as soon as we gather evidence, and it will go through due process of law," she said.

"There was one attack on a police outpost as late as yesterday, when one policeman was killed, and there have been Muslims killed as well since the attacks began on the ninth of October.

"We have not tried to hide any of this. We are trying to get to the bottom of the matter."

Aid agencies say more than 15,000 people have been displaced since the military took control of an area close to the Bangladesh border, home to the stateless Rohingya minority.

Foreign diplomats briefed media on Friday after returning from a visit to the flashpoint area, where the military has barred international observers since the border post attacks.

UN resident and humanitarian coordinator Renata Dessallien said the government had agreed to allow aid into the region, where an estimated 150,000 people are without their usual assistance.

"The government agreed to that all previous ongoing humanitarian development assistance could start," she told journalists.

Suu Kyi, who wraps up her five-day visit to Japan on Saturday, said the diplomats were expected to file a report on their findings.

"I think when you hear from them you will have a more balanced idea of what is going on there," she said.

"We have been very careful not to blame anybody in particular unless we have complete evidence as to who was responsible for what."

During Friday's press conference, Suu Kyi also thanked Japan for its aid and encouraged the strengthening of the bilateral ties.

Prime Minister Shinzo Abe has pledged to offer aid and investments totalling almost $8 billion over five years to help development and democratisation in Myanmar.