The US Coast Guard has set fire to part of a big oil slick in the Gulf of Mexico, in an attempt to save environmentally fragile wetlands.

The “test burn” is taking place in an area about 30 miles (50km) east of the Mississippi river delta, officials say.

About 1,000 barrels (42,000 gallons) of oil a day have been leaking into the sea from a well since an explosion on a drilling rig off Louisiana last week.

Officials fear the leak could cause one of the worst oil spills in US history.

An investigation has been ordered into the incident, which is believed to have left 11 of the rig’s workers dead. They are still missing.