Operations carried out against Rohingya Muslims in Burma had “all the hallmarks” of ethnic cleansing, a US senator has said.

The country’s leader, Aung San Suu Kyi, has continued to express doubts about allegations of human rights abuses. But members of the US Senate have said they were troubled by a “violent and disproportionate” security response to Rohingya militant attacks that have driven more than 600,000 people from Burma to neighbouring Bangladesh.

Human rights groups have accused Burma’s military of atrocities, including mass rape, against the stateless Rohingya during so-called clearance operations.

Burma says the operation, which the United Nations has also likened to a “textbook example of ethnic cleansing”, was necessary for national security after Rohingya militants attacked 30 security posts and an army base in the state in August.

“We are not hearing of any violations going on at the moment,” Ms Suu Kyi told reporters at the Asia-Europe Meeting in Burma’s capital Naypyidaw.

“We can’t say whether it has happened or not. As a responsibility of the government, we have to make sure that it won’t happen.”

The government in mostly Buddhist Burma views the Rohingya as illegal immigrants from Bangladesh.

In early November, members of the US Congress proposed targeted sanctions and travel restrictions on Burma’s military officials.

Democratic Senator Jeff Merkley, who was among the sponsors of the legislation, led a congressional delegation that visited Rakhine, a state in Burma located on the western coast.

Rohingya refugees – in pictures Show all 15 1 /15 Rohingya refugees – in pictures Rohingya refugees – in pictures A young girl and a baby wade through mud after arriving in Whaikhyang, Bangladesh from Burma on 10 September Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya refugees walk through a camp in Whaikhyang, Bangladesh after arriving from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures A young Rohingya refugee gathers firewood after arriving in Whaikhyang, Bangladesh from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya refugees wait for sacks of rice to be distributed in Whaikhyang, Bangladesh Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees arrive on a boat in Whaikhyang, Bangladesh after crossing from Burma on 8 September Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees react after being re-united with each other after arriving in Whaikhyang, Bangladesh on a boat from Burma Getty Rohingya refugees – in pictures Rohingya Muslim refugees walk along the remains of a road after arriving in Whaikhyang, Bangladesh on a boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees wade through water after arriving in Whaikhyang, Bangladesh by boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees wade through water after arriving in Whaikhyang, Bangladesh by boat from Myanmar Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees stand in the rain after arriving in Whaikhyang, Bangladesh by boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Indian children hold placards and shout slogans during a protest against the alleged persecution of the Rohingya Muslims in Burma EPA/Raminder Pal Singh Rohingya refugees – in pictures Supporters of the Difa-e-Pakistan Council (DPC), an Islamic organisation, listen to their leaders' speeches against Burma's persecution of Rohingya Muslims, during a demonstration in Karachi Reuters/Akhtar Soomro Rohingya refugees – in pictures Hundreds of Iranians take part in a protest against violence in Myanmar after weekly Friday prayers, in Tehran EPA/Abedin Taherkenareh Rohingya refugees – in pictures Indonesian Muslim activists hold placards and shout slogans during a protest against the alleged persecution of the Rohingya minority in Magelang, Central Java, Indonesia EPA/Ali Lutfi Rohingya refugees – in pictures Members of an Islamic organisation shout slogans against the Burma government during a protest in Dhaka, Bangladesh EPA

The group also travelled to Cox’s Bazar district in Bangladesh, where Rohingya refugees are residing in makeshift camps and fed by overstretched aid agencies.

“Many refugees have suffered direct attacks including loved ones, children and husbands being killed in front of them, wives and daughters being raped, burns and other horrific injuries. This has all the hallmarks of ethnic cleansing,” Mr Merkley told reporters.

“We are profoundly disturbed by the violent and disproportionate response against the Rohingya by the military and local groups,” he said.

The delegation called for Burma to allow an international investigation into the alleged atrocities.

“We want to emphasise that the world is watching,” Mr Merkley said, adding that it was important Burma allowed anyone who wants to come back to return to their homes and their farms.

Mr Merkley said the delegation was “not here today to recommend what the US government would do or should do”, when asked about the legislation introduced in Congress.

Ms Suu Kyi’s civilian government has been heavily criticised for its response to the crisis. However, it has no control over the generals it shares power with following decades of military rule.

The Burmese leader has said she hopes to talk with Bangladesh’s foreign minister this week about an agreement that could lead to the “safe and voluntary return” of those who have fled.