BP has pledged USD1 billion to jump-start projects aimed at restoring the US Gulf Coast after last year\'s massive oil spill, officials said Thursday.

A shrimp boat trolls for its catch on April 19, near Middle Ground in southern Louisiana.

"The agreement in no way affects the ultimate liability of BP or any other entity for natural resource damages or other liabilities, but provides an opportunity to help restoration get started sooner," the US Justice Department said in a statement.

The Justice Department called it a "first step" towards fulfilling BP\'s obligations to fund the "complete restoration of injured public resources."

A formal damage assessment is expected to take years to complete and will likely be subject to legal wrangling as BP seeks to spread the liability among its well ownership partners and subcontractors.

Earlier, the British energy giant announced a USD40-billion lawsuit against rig operator Transocean, which then unveiled a countersuit.

The restoration agreement came a day after the first anniversary of the Deepwater Horizon disaster, which unleashed the biggest maritime oil spill in history.

The money will be used to rebuild damaged coastal marshes, replenish soiled beaches, conserve ocean habitat to help injured wildlife recover and restore barrier islands and wetlands that provide natural protection from storms.

"This milestone agreement will allow us to jump-start restoration projects that will bring Gulf Coast marshes, wetlands, and wildlife habitat back to health after the damage they suffered as a result of the Deepwater Horizon spill," Secretary of the Interior Ken Salazar said in a statement.

Oil-coated dolphin carcasses and sticky tar balls continue to wash up on beaches a year after the explosion which killed 11 workers and sank the Deepwater Horizon rig some 50 miles (80 kilometers) off the coast of Louisiana.

By the time the well was capped 87 days later, 4.9 million barrels (206 million gallons) of oil had gushed out of the runaway well 5,000 feet (1,500 meters) below the surface of the Gulf of Mexico.

Hundreds of miles of fragile coastal wetlands and beaches were contaminated, a third of the Gulf\'s rich US waters were closed to fishing, and the economic costs have reached into the tens of billions.

"BP believes early restoration will result in identified improvements to wildlife, habitat and related recreational uses in the Gulf, and our voluntary commitment to that process is the best way to get restoration projects moving as soon as possible," said Lamar McKay, chairman and president of BP America.

"Our voluntary agreement to accelerate restoration projects builds upon the cooperative approach BP has taken toward working with Gulf communities and regulators since the accident, and in assessing the potential injury to natural resources."

BP took a USD40.9-billion charge in 2010 related to the spill -- including USD13.6 billion for the massive spill response -- and warned shareholders that it could not fully estimate its future liabilities.

It is the subject of a potentially criminal federal investigation and could face massive fines and penalties in addition to its legal obligation to restore environmental damage.

The company has also set up a USD20-billion trust fund to cover compensation claims from fishermen and others affected by the spill and has so far paid out USD3.9 billion to 179,000 claimants.

In addition to the suit against Transocean, BP has also sued oil services giant Halliburton, which was responsible for the well\'s flawed cement job, and parts manufacturer Cameron, which supplied the faulty blowout preventer.

A presidential commission tasked with investigating the spill blamed the disaster on management failures by BP, Halliburton and Transocean.

US investigators said last month that the well might never have blown if the company\'s engineers had been consulted about a key test that pointed to defective cementing of the well.

Meanwhile, BP\'s woes deepened on Thursday when the local tycoons of its Russian joint venture announced plans to sue the British energy giant over its bid to forge an alliance with state firm Rosneft.