Suu Kyi, who held her first talks with a minister in the new government on Monday, said reconciliation between state forces and armed ethnic minority rebel groups could not be achieved by "military means".

"I would like to earnestly call for an immediate ceasefire and the peaceful resolution of the conflicts for the benefit of all ethnicities in the Union of Myanmar," she said in the letter, also addressed to ethnic groups.

Myanmar - where power was handed to a nominally civilian government in March after almost 50 years of military rule - has been plagued by decades of civil war. Fighting has intensified in the north and east of the country in recent months.

Suu Kyi was released from house arrest days after the controversial election last November and has since been warned to stay out of politics.

In her letter, she said she was willing to get involved in halting the unrest.

"I am ready to do as much as I can to support the ceasefire and the peace process," she said.

The Nobel Peace Prize winner addressed the letter directly to Myanmar president Thein Sein, a former general who took power after the poll, having previously communicated only through her National League for Democracy (NLD).

She has shown increasing confidence in recent weeks, testing the limits of her freedom with her first trip outside Yangon earlier this month and leading hundreds of people in a memorial to her father on her return to the city.

A source from the NLD said Suu Kyi is planning another trip at the beginning of next month, although the outing has not been finalised and it is not clear whether the visit will be political or personal.

"She will go to meditate at a monastery in Yangon for about three days, after that she is likely to go to Bago," the source said, referring to a region north of Yangon. The NLD was not able to officially confirm any details.

Suu Kyi has spent much of the last two decades in detention, and some observers believe the government would be quick to limit her freedom again if she is perceived as a threat to their rule.

She refrained from overt political activities that might have antagonised the government during her four-day excursion to Bagan, following warnings that "chaos and riots" could ensue if she went ahead with a planned political tour.

Suu Kyi spent more than an hour with labour minister Aung Kyi on Monday in what he described as the "first step towards many things to be worked on in the future".