Malaysia's prime minister said Thursday that he had ordered the navy and the coast guard to comb the sea looking for stranded migrants, the first country to announce it will search for the refugees instead of waiting for them to wash up on Southeast Asia's shores.

As the region's migrant crisis enters its fourth week, it remains unclear how many vulnerable people are adrift at sea but aid groups and the U.N. say there could be thousands and time is running out to save them.

In the past three weeks, more than 3,000 people — Rohingya Muslims fleeing persecution in Myanmar and Bangladeshis trying to escape poverty — have landed in overcrowded boats on the shores of Indonesia, Malaysia and Thailand. Aid groups estimate that thousands more are adrift on vessels without food and water, following a crackdown on human traffickers that prompted captains and smugglers to abandon their boats.

Malaysia initiated a series of talks this week to try to ease the humanitarian crisis, and announced Wednesday that Malaysia and Indonesia will offer temporary shelter to thousands of the incoming migrants. It was seen as a major breakthrough, after weeks of saying the migrants weren't welcome. But rights groups said the proposal addressed only part of the problem, and urged countries to start actively searching for those stranded at sea.

Malaysian Prime Minister Najib Razak addressed the concern via Twitter on Thursday, ordering the navy and coast guard "to conduct search and rescue efforts (for) Rohingya boats. We have to prevent loss of life."

Meanwhile, the foreign minister of Malaysia was scheduled to visit Myanmar on Thursday to discuss the crisis. The ministry issued a delicately worded statement saying the two would "exchange views on irregular movements of people ... in Southeast Asia," using politically correct language so as not to offend Myanmar — which refuses to shoulder any blame for the crisis or discuss the matter if the word "Rohingya" is mentioned.

The U.N. says the Rohingya are one of the most persecuted groups in the world. Neither Myanmar nor Bangladesh recognizes them as citizens. In Buddhist-majority Myanmar, officials refer to the group as "Bengalis" and insist they are illegal immigrants from Bangladesh, even though most have lived in the country for generations.

Over the past few years, Myanmar's Rohingya have faced increasing state-sanctioned discrimination. They have been targeted by violent mobs of Buddhist extremists and confined to camps. At least 120,000 have fled to sea, and an unknown number have died along the way.

While Indonesia and Malaysia said Wednesday they would temporarily take in some refugees, they also appealed for international help, saying the crisis is a global, not a regional, problem.

"This is not an ASEAN problem," Malaysian Foreign Minister Anifah Aman said Wednesday, referring to the 10-nation grouping of Southeast Asian countries. "This is a problem for the international community."

Anifah hosted Wednesday's emergency meeting with the foreign ministers of Indonesia and Thailand, and the three countries issued a joint statement saying Malaysia and Indonesia had "agreed to offer temporary shelter provided that the settlement and repatriation process will be done in one year by the international community."

Indonesian Vice President Jusuf Kalla said his government was ready to shelter Rohingya for one year, while the Bangladeshis would be sent back home. "A year is (the) maximum," he said. "But there should be international cooperation."

So far there have been two offers from the international community.

In Washington, the State Department said Thursday the United States was also willing to take in Rohingya refugees as part of international efforts to cope with the crisis. Spokeswoman Marie Harf said that the U.S. is prepared to take a leading role in any multicountry effort, organized by the United Nations refugee agency, to resettle the most vulnerable refugees.

The tiny African country of Gambia has also said it was willing to take in Rohingya refugees. "As human beings, more so fellow Muslims, it is (our) sacred duty to help," the presidency said in a statement.

The reversal of Malaysia's and Indonesia's positions, after weeks of saying the migrants were not welcome, came as more than 430 weak, hungry people were rescued Wednesday — not by navies patrolling the waters but by a flotilla of Indonesian fishermen who brought them ashore in the eastern province of Aceh.

The U.N. refugee agency believes there are 4,000 still at sea, although some activists put the number at 6,000.

The No. 2 U.S. diplomat, currently visiting Southeast Asia, said he will raise the humanitarian crisis of the Rohingya when he meets with senior Myanmar government leaders on Thursday.

"The only sustainable solution to the problem is changing the conditions that let them put their lives at risk at the first place," Deputy Secretary of State Anthony Blinken told reporters in Jakarta.

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Gecker contributed reporting from Bangkok, and Associated Press writer Matthew Pennington in Washington contributed to this report.