Aung San Suu Kyi on Thursday described violence in west Myanmar between Buddhists and Muslims as a "huge international tragedy" and said illegal migration from Bangladesh had to be stopped.
Suu Kyi, on a visit to neighbouring India, said she had declined to speak out on behalf of stateless Rohingya Muslims who live on both sides of the border as she wanted to promote reconciliation after recent bloodshed.
More than 100,000 people have been displaced in Myanmar since June in two major outbreaks of violence in the western state of Rakhine, where renewed clashes last month uprooted about 30,000 people.
Dozens have been killed on both sides and thousands of homes torched.
"Don't forget that violence has been committed by both sides, this is why I prefer not to take sides and also I want to work towards reconciliation," she told the NDTV news channel.
"Is there a lot of illegal crossing of the border (with Bangladesh) still going on? We have got to put a stop to it otherwise there will never be an end to the problem," she said.
The Nobel laureate, who was released from military house arrest in 2010, has caused disappointment among international supporters for her muted response to the ethnic violence in her homeland.
"This is a huge international tragedy and this is why I keep saying that the government must have a policy about their citizenship laws," she said.
Myanmar's 800,000 Rohingya are seen by the government and many in the country as illegal immigrants from neighbouring Bangladesh. They face severe discrimination that activists say has led to a deepening alienation.
"There are quarrels about whether people are true citizens under law or whether they have come over as migrants later from Bangladesh," she said.
"Most people seem to think there is only one country involved in this border issue.
"There are two countries. There is Bangladesh on one side and Burma (Myanmar) on the other and the security of the border surely is the responsibility of both countries."
The Rohingya, who make up the vast majority of those displaced in the fighting, are described by the UN as among the world's most persecuted minorities.