Myanmar- also known as Burma -said its navy had seized a vessel off its coast with more than 700 migrants off its southern coast.
Just as the meeting of Southeast Asian nations was wrapping up in Bangkok on Friday, Myanmar's Ministry of Information announced its navy had intercepted a boat with 727 migrants aboard and was taking them to a base on an island off its southern coast to determine their identity.
It said the migrants - more than 600 men, along with women and children - were "Bengali", reported BBC.
The term is used to describe both describe Myanmar's persecuted Rohingya minority as well as immigrants from Bangladesh.
It came a week after Myanmar intercepted 200 migrants - its first such rescue, which came amid criticism the country has failed to enough to help those stranded and stem the crisis.
In Friday's meeting, the nations concerned agreed to intensify search and rescue efforts to help vulnerable "boat people" stranded in the region's seas.
Countries affected by the crisis agreed at the meeting in Bangkok to set up an anti-trafficking task force, and approved a wide-ranging list of recommendations to tackle the "root causes" of the crisis - although the plan was carefully worded to avoid upsetting Myanmar, which denies it is the source of the problem.
"That the summit took place at all with this wide participation is itself a good result," William Lacy Swing, director general of the International Organisation for Migration (IOM), told Reuters.
"It's a very important first step. Having Myanmar there was key. I'm pretty optimistic. We're pleased that they've retained an emphasis on intensifying search and rescue operations."
While some of the migrants are Bangladeshis escaping poverty at home, many are members of Myanmar's 1.1 million Rohingya Muslim minority who live in apartheid-like conditions in the country's Rakhine state.
"You cannot single out my country," Htein Lin, director general at Myanmar's Ministry of Foreign Affairs and head of the country's delegation, had said in his opening remarks. "In the influx of migration, Myanmar is not the only country."
Myanmar does not consider the Rohingya citizens, rendering them effectively stateless, while denying it discriminates against them or that they are fleeing persecution. It does not call them Rohingya but refers to them as Bengalis, indicating they are from Bangladesh.
Friday's talks include representatives from 17 countries affected by "irregular migration in the Indian Ocean".
The US, Japan and Switzerland have sent observers and there are officials from the UN refugee agency UNHCR, the UN Office on Drugs and Crime and the International Organization for Migration.
However, correspondents say many of those attending are not ministerial-level and the talks are unlikely to produce a binding agreement or even a plan of action.
Alice Budisatrijo reports from a shelter in Indonesia for migrants from Myanmar and Bangladesh
Most countries are unwilling take in the migrants, fearing that by accepting them they will encourage more to make the journey.
Malaysia and Indonesia have agreed to stop towing boats out to sea and to give temporary shelter to those who have landed. Thailand has only said it will stop rejecting the boats.
More than 4,000 migrants have landed in Indonesia, Malaysia, Thailand, Myanmar and Bangladesh since Thailand launched a crackdown on people-smuggling gangs this month.
Around 2,000 may still be adrift in boats on the Andaman Sea and Bay of Bengal, the United Nations said.