Families poured onto Myanmar's streets in 2015 when her National League for Democracy won historic elections in a landslide, supposedly ending half a century of brutal military rule.

But now when Ms Suu Kyi travels abroad she faces awkward questions about her silence on the plight of Rohingya Muslims and atrocities committed on them in her country's western Rakhine State that the United Nations says could amount to "genocide" and "crimes against humanity."

Visiting Belgium this week, Ms Suu Kyi clashed with the European Union's top diplomat Federica Mogherini, who urged her to support a United Nations mission to investigate the Rohingya atrocities.

"The fact-finding mission is focussing on establishing the truth about the past," Ms Mogherini told a press briefing, standing alongside Myanmar's de factor leader, who is also her country's foreign minister.

"We believe this can contribute to establishing the facts."

But Ms Suu Kyi again ruled out Myanmar co-operating with the investigation that was set-up in March after Australia co-sponsored a motion at the 47-member UN Human Rights Council in Geneva.

"We are disassociating ourselves from the resolution because we don't think the resolution is in keeping with what is actually happening on the ground," she said.

A devastating UN report in February detailed a "calculated policy of terror" by Myanmar security forces in Rakhine that included the slitting of a baby's throat, the stomping on a woman's stomach while she was in labour and the locking of families in homes which were set-alight.

In earlier comments Ms Suu Kyi, the daughter of Myanmar's independence hero Aung San, denied ethnic cleansing was taken place in Rakhine.

"It is a matter of different sides of the divide, and this divide we are trying to close up," she said.

Ms Suu Kyi has also played down the notion she was an icon, declaring herself "just a politician" and that required making "principled compromises."

Myanmar's Senior-General Min Aung Hlaing has also rejected the UN findings and described more than a million Rohingya in Rakhine as "Bengali" interlopers, despite that they have been living in Buddhist-majority Myanmar for generations.

Diplomats say the UN's investigation will be compromised unless the military allows investigators to go to Rakhine, which has been closed to outsiders since October when security forces violently swept through towns and villages, after attacks on several police border posts.

Ms Suu Kyi also this week declined an invitation to meet US Secretary of State Rex Tillerson alongside other foreign ministers in the 10-member Association of South-East Asian Nations, in Washington on Thursday.

Zaw Htay, an official in Ms Suu Kyi's office, said she had another appointment that day in Europe and a senior official would be sent to attend the meeting.

Asked by journalists whether Ms Suu Kyi's absence in Washington indicated Myanmar's ties with the US had cooled, in favour of China, Myanmar's foreign affairs secretary Kyaw Zeya said: "We don't promote relations with any country at the expense of another."

As international criticism of Ms Suu Kyi has grown a number of her supporters have leapt to her defence, pointing to the serious problems facing Myanmar when she took power just a little over 12 months ago.

They say the real blame for the Rakhine atrocities and attempts to cover them up lies with the country's powerful military which continues to control key security ministries.