HOUSTON, May 26 (Xinhua) -- BP started a so-called "top kill" operation Wednesday afternoon in an attempt to plug a undersea gusher in the Gulf of Mexico.

The pumping of plugging agents into the site of the leak began at 1 p.m. (CDT) and continues, BP said in a statement.

The procedure is intended to stem the flow of oil and gas and ultimately kill the well by injecting heavy drilling fluids through the blow out preventer on the seabed, down into the well, BP said.

A frame grab, taken from a BP live video feed, shows activity during the "top kill" procedure to stop the flow of oil from the Gulf of Mexico oil well May 26, 2010. BP Plc launched an ambitious deep sea operation to choke off a gushing oil leak in the Gulf of Mexico on Wednesday, but President Barack Obama cautioned Americans there was no guarantee it would work.