The FBI is conducting a criminal investigation into the deadly collapse of Baltimore’s Francis Scott Key Bridge, according to sources.

It is understood that the probe is focused on the circumstances leading up to the incident in the state of Maryland and whether all US federal laws were followed.

The FBI was present aboard the cargo ship Dali to conduct court-authorised law enforcement activity, the agency said in a statement.

The investigation was first reported by the Washington Post, with sources confirming the probe to the Associated Press.

Separately, Baltimore mayor Brandon Scott announced a partnership with two law firms to “launch legal action to hold the wrongdoers responsible” and mitigate harm to city residents over the incident.

The container ship Dali left Baltimore’s port in the early hours of March 26, laden with cargo and headed for Sri Lanka, when it struck one of the bridge’s supporting columns, causing the span to collapse into the Patapsco River and sending six road workers plunging to their deaths.

Divers have recovered three bodies from the underwater wreckage, while the remaining three victims are still unaccounted for.

National Transportation Safety Board chairwoman Jennifer Homendy said last week that investigators are focusing on the electrical power system of the massive container ship that veered off course.

The ship experienced power issues moments before the crash, as evidenced in videos showing its lights going out and coming back on.

Ms Homendy said information gleaned from the vessel’s voyage data recorder is relatively basic, “so that information in the engine room will help us tremendously”.

Monday’s statement from Baltimore said the city “will take decisive action to hold responsible all entities accountable for the Key Bridge tragedy, including the owner, charterer, manager/operator, and the manufacturer of the M/V Dali, as well as any other potentially liable third parties”.

“We are continuing to do everything in our power to support everyone impacted here and will continue to recognise the human impact this event has had,” Mr Scott said in a statement.

“Part of that work needs to be seeking recourse from those who may potentially be responsible, and with the ship’s owner filing a petition to limit its liability mere days after the incident, we need to act equally as quickly to protect the City’s interests.”