Barack Obama has instructed the Department of Justice to monitor the reaction of law enforcement authorities in Missouri in the aftermath of the shooting dead by police of an unarmed 18-year-old, but has so far stopped short of ordering a more dramatic federal intervention.

After four nights of violent disturbances in the city of Ferguson, the president on Thursday did not go as far as to condemn local police and appealed for calm from all sides, but urged the state governor, Jay Nixon, to ensure the official response was proportionate.

Obama said he had asked the attorney general, Eric Holder, to provide a report on the crisis, adding to an existing FBI investigation into possible civil rights violations during the death of Michael Brown last weekend.

“Now is the time for an open and transparent process to see that justice is done, and I have asked that the attorney general and the US attorney on the scene to continue to work with local officials to move that process forward,” said Obama. “They will be reporting to me in the coming days about what’s being done to make sure that happens.”

The heavy-handed police response to protests in Ferguson prompted growing political anger in Washington on Thursday, including calls from the veteran civil rights activist and congressman John Lewis for the White House to send in national guard troops under federal control to take over local policing and ensure protesters were protected.

“This is not China or Russia or Syria,” said Lewis. “This is America, and in this country we have a right to protest in an orderly non-violent fashion.”

He compared the need for some “martial law” to restore trust in Ferguson to President Kennedy’s decision to send federal marshals to Montgomery, Alabama, during violent civil rights protests that Lewis took part in during 1961.

Similar moves were taken by President Johnson in 1965 when he sent the national guard into Selma, Alabama, under direct control from Washington to protect marchers from local police.

The last time the national guard was “federalised”, or put under the control of the president rather than state governors, was in 1992 during the Los Angeles riots that followed the beating of Rodney King by LA police officers.

In total, national guard troops have only been sent in to deal with domestic crises in this way on ten occasions since the second world war – mostly to help protect civil rights protesters in the 1950s and 1960s.

Such a move in this instance is likely to add to fears of an overly militarised response by police, however. Though the national guard has units of military police who are trained to deal with civil disturbances, 90% of its members are made up of part-time volunteers who would have to be called up and may rely on similar equipment to that currently used by Ferguson police.

Previous presidents have largely used executive orders to make deployments, something that Obama has currently shown no sign of wanting to do in this instance.

Facebook Twitter Pinterest A man watches as police walk through a cloud of smoke during a clash with protesters on Wednesday night. Photograph: Jeff Roberson /AP

Instead, the White House seems to be relying on the civil rights division of the Department of Justice to oversee actions by state and county police in Ferguson as well as the local office of the Federal Bureau of Investigations.

The FBI confirmed it was already taking a lead role in investigating potential civil rights violations connected with the death of Michael Brown in Ferguson but was currently providing a support role for police in responding to the protests that followed.

“We are the lead investigative organisation for federal civil rights violations, which is why we opened a separate case,” Cheryl Mimura, a spokeswoman for the FBI’s St Louis field office, told the Guardian.

“But there are a lot of overlapping [alleged] violations, so it depends on when the investigations are complete which prosecuting agency is going to have the evidence to support an actual charge.”

She declined to say how many federal officers were involved, citing safety concerns and threats against law enforcement, but revealed that FBI intelligence analysts were also assisting local and state police deal with public order problems.

“I wouldn’t say we have agents handling riot control, that not’s something we would do unless the scale of it continues to grow, but we do have agents providing support – on the investigative end of it and just looking at the intelligence, for example Anonymous claiming hack attacks against the police department,” added Mimura.

Civil rights activists said the crisis pointed to the need for greater national monitoring of racial discrimination by police.

“The tragic shooting of Michael Brown and the events in Ferguson underscore the gap between what our constitution requires and our society is currently confronting in terms of race discrimination,” said Chandra Bhatnagar, senior staff attorney at ACLU Human Rights Programme.

Ejim Dike, director of US Human Rights Network, added: “In addition to a legal response from the Department of Justice, there is a need for moral and political leadership from the executive branch, from Obama and Holder. We think the federal government should show moral leadership by making clear statements about what policing should look like.”

Other national politicians, including the Republican senator Rand Paul, criticised what they called an already overly militarised police response in Ferguson and linked it to government abuse of individual rights in wider cases.

“When you couple this militarisation of law enforcement with an erosion of civil liberties and due process that allows the police to become judge and jury – national security letters, no-knock searches, broad general warrants, pre-conviction forfeiture – we begin to have a very serious problem on our hands,” said Paul in an opinion column for Time magazine.