BP plans to keep the ruptured oil well in the Gulf of Mexico shut until an operation to finally "kill" it begins at the end of July, an official saidto day.

"We're hopeful that if the encouraging signs continue we'll be able to continue the integrity test all the way to the point where we get the well killed," BP chief operating officer Doug Suttles told journalists.

BP's planned "kill" operation, to finally plug the runaway well with heavy drilling fluids and then cement it, is scheduled to begin at the end of July -- once a relief well has been finished -- and take until mid-August.