Burma’s president has signed off on a law requiring some mothers to space their children three years apart despite international objections that it could be used to repress women and minorities such as the Rohingya Muslims now fleeing the country for other parts of south-east Asia.

The population control health care bill — drafted under pressure from hard-line Buddhist monks with a staunchly anti-Muslim agenda — was passed by parliamentarians last month.

US deputy secretary of state Anthony Blinken said he warned Burma’s leaders during face-to-face talks last week about the dangers of the bill. On Saturday, hours after the diplomat left, state-run media announced president Thein Sein had signed it into law.

As predominantly Buddhist Burma started moving from dictatorship to democracy four years ago, newfound freedoms of expression lifted the lid on deep-seeded hatred for minority Muslims — including Rohingya now arriving on south-east Asian shores in crowded, rickety boats.

Many are fleeing persecution and violence that has left up to 280 people dead and forced another 140,000 from their homes in western Rakhine state. They are living under apartheid-like conditions in dusty, crowded camps, with little access to education or adequate medical care. They also have little freedom of movement, having to pay hefty bribes if they want to pass police barricades, even for emergencies.

The population law — which carries no punitive measures — gives regional authorities the power to implement birth-spacing guidelines in areas with high rates of population growth.

Though the government says the law is aimed at bringing down maternal and infant mortality rates, activists argue that it steps on women’s reproductive rights and can be used to suppress the growth of marginalised groups.

Hard-line Buddhists have repeatedly warned that Muslims, with their high birthrates, could take over the country of 50 million even though they currently represent less than 10% of the population.

“It’s very disappointing,” Khin Lay, a women’s rights activist, said of the president’s decision to sign off on the law. “If the government wants to protect women, they should strengthen laws already in place to do that.”

Blinken, who met with Thein Sein, the army’s commander in chief and other government officials during a two-day visit to Burma, said he expressed “deep concern” about the law and three others in the assembly aimed at protecting race and religion.

“The legislation contains provisions that can be enforced in a manner that would undermine reproductive rights, women’s rights and religious freedom,” Blinken told reporters Friday. “We shared the concerns that these bills can exacerbate ethic and religious divisions and undermine the country’s efforts to promote tolerance and diversity.”