The US federal authorities have opened criminal and civil investigations into the massive oil spill in the Gulf of Mexico, US Attorney General Eric Holder said Tuesday.

"We will closely examine the actions of those involved in the spill. If we find evidence of illegal behavior, we will be extremely forceful in our response," Holder was quoted by U.S. media as saying in New Orleans, Louisiana.

Holder headed to the Gulf coast Tuesday to survey the oil spill unleashed by the explosion of BP-leased Deepwater Horizon drilling rig off the Louisiana coast late April.

Holder would also meet with state attorneys general and federal prosecutors from Louisiana, Alabama and Mississippi, which are threatened by the unfolding Gulf oil spill, according to media reports.

A group of senators sent Holder a letter last month expressing concerns about the truthfulness and accuracy of statements submitted by BP to the government in its initial exploration plan for the site of the drilling, and asking Holder to investigate possible criminal and civil wrongdoing.

The oil spill from BP's offshore well has surpassed the 1989 Exxon Valdez to be the worst in U.S. history, spewing oil at a rate of 12,000 to 25,000 barrels a day.

BP lost billions in market value when shares plummeted in the first trading day since it failed in its "top kill" effort, which is considered the best chance for it to plug the undersea gusher quickly.

BP on Tuesday began sawing into the damaged pipe and preparing to place a cap over the spill to siphon most of the runaway oil.