WASHINGTON — Senate Democrats are calling for the Obama administration to improve inspections of deepwater oil rigs such as the one that exploded last month in the Gulf of Mexico. The lawmakers said oil companies should pay for the emergency inspections, not taxpayers.

The blast killed 11 people and has spilled millions of gallons of oil.

In a letter Wednesday to President Barack Obama, Senate Majority Leader Harry Reid and other Democrats urged immediate and enhanced inspections of all offshore drilling rigs and platforms that could pose a significant environmental threat.

The letter, signed by the top five Democratic leaders, said inspections by the Minerals Management Service of the Deepwater Horizon oil rig were inadequate. The inspections failed to reveal problems with the so-called blowout preventer, among other problems, the letter said.

The lawmakers called for Obama and Interior Secretary Ken Salazar to conduct an "immediate top-to-bottom review of all inspection and testing procedures used to evaluate all offshore drilling equipment," including on offshore rigs and production platforms.

"We need foolproof testing procedures to guarantee equipment integrity, particularly when it comes to equipment like a (blowout preventer) that must act as the last line of defense against disaster," they said.

White House spokesman Ben LaBolt said Interior Department workers inspected all deepwater platforms in the Gulf, following a directive from Salazar last month.

Kendra Barkoff, a spokeswoman for Salazar, said the Minerals Management Service has completed its inspections of all 30 deepwater drilling rigs in the Gulf. The inspections focused on blowout preventers and on making sure well-control drills were performed as required by regulations, Barkoff said.

Inspectors found violations on two rigs that have since been corrected, she said.

Monthly inspections of working drilling rigs will continue, she added. The minerals agency conducts about 29,000 inspections per year.

On the payment issue, a spokesman for Sen. Robert Menendez, D-N.J., said the federal government should adopt a reimbursement system similar to oil spill cleanup. The Coast Guard and other federal agencies are working to clean up and contain the oil spill, but will be reimbursed by BP PLC, the oil giant that was operating the Deepwater Horizon rig. A similar system could be created for inspections, said Afshin Mohamadi, a spokesman for Menendez.

Associated Press writer Erica Werner contributed to this report.