Salvadoran President Jose Napoleon Duarte underwent surgery Tuesday to remove cancerous tissue from his stomach, and the Salvadoran ambassador called the operation a qualified success.

Duarte will remain in guarded condition at Walter Reed Army Medical Center for the next 30 days, said Salvadoran Ambassador Ernesto Rivas Gallont.Rivas Gallont said doctors removed three-quarters of Duarte's stomach. The surgeons had considered removing cancerous tissue from his liver but decided to leave it untouched, the ambassador said.

"It was a success," he said. "Of course one would have to qualify that statement because it is cancer."

The ambassador said doctors were "afraid the cancer might have expanded beyond the liver, but apparently it has not."

A statement from hospital officials was not immediately available.

Earlier in the day, Alfredo Milian, economics adviser at the Salvadoran Embassy, said the procedure, which began at 7 a.m. and ended around noon, was "a very serious operation since it has a high risk involving vital organs."