MEXICO CITY - The United States and Mexico have agreed to extend a treaty on holding off from drilling oil close to their shared border in the Gulf of Mexico for a further three years, Mexico's Foreign Ministry said on Wednesday.

It is the second time the two nations have agreed to extend the pact that covers an area commonly known as the "doughnut hole" that lies outside both countries' 200 nautical mile territorial limits in the Gulf of Mexico.

Oil drilling in shared water areas has been a hot issue in Mexico since 2000 when then-President Vicente Fox accused the US of sucking up natural gas from exploration wells that cross under their shared border and selling it back to Mexico across the top.

"No entity has recorded the presence of any cross-border deposit, but we consider it important to have a regime of rules with a bilateral character in case a discovery should occur in the future," said the statement.

The ministry said the latest agreement was a follow-up to the work done by President Felipe Calderon and President Barack Obama when they met on May 19 in Washington.

Mexico is not capable of exploring at the water depths in the area covered by the treaty due to lack of technology at Petroleos Mexicanos (Pemex), the only firm allowed to explore or exploit hydrocarbons on Mexican territory.

There are plenty of firms on the US side that can explore deep waters in the Gulf of Mexico, but such exploration activity has caused a massive ecological disaster this year.

On April 20, a gas explosion on a rig called the Deepwater Horizon triggered an oil spill that is leaking thousands of barrels of oil into the Gulf of Mexico per day.