THE HAGUE, Netherlands-A former U.N. interpreter took the stand Thursday with her identity concealed as the first prosecution witness in the trial of three Croat generals accused of orchestrating a 1995 campaign of murder and persecution of Serbs.

She testified that she was forced to flee to a bomb shelter as shells rained down on the town of Knin in the early morning of Aug. 4, 1995, during the deadly opening of a Croatian army blitz known as Operation Storm.

The operation snatched back a region known as the Krajina seized four years earlier by rebel Serbs as the former Yugoslavia crumbled. It is widely regarded as a military triumph in Croatia and the three generals on trial here, Ante Gotovina, Mladen Markac and Ivan Cermak, are considered national heroes.

But prosecutors say the operation began with the shelling of Knin and continued through August and September with a brutal campaign in which Croat forces murdered Serb villagers, torched their houses, killed their livestock and poisoned their wells.

By the end of Operation Storm some 350 Serbs were dead and up to 200,000 had fled the region.

Gotovina, Markac and Cermak have pleaded not guilty to charges of crimes against humanity and war crimes based on their command of troops and special forces involved in the killings and persecution.

The woman testifying Thursday was identified only as Witness 136 and her face was hidden from people watching the trial in the courtroom or on television or the Internet.

Most of her testimony was presented to the three-judge panel in two written statements. Prosecutors questioned her only briefly on her experiences during and after the shelling of Knin.

Describing how she fled her third-floor apartment in terror during the shelling, the witness said: "As soon as I left the building, a house next to the apartment building was completely destroyed and I wondered at the time if anybody could have survived."

She also described visiting a cemetery in Knin a few days after the shelling and counting 62 new graves, most of them unidentified.

Under cross examination from Gotovina's American lawyer Greg Kehoe, the witness said shells hit homes and a medical clinic.

"I cannot recall any other details," she said. "As I ran, shells were falling around me."

In an attempt to justify the shelling, Kehoe told the witness that the area where the shells fell was "replete with various army ... facilities."

Under international law, shelling military targets is allowed but care must be taken not to cause civilian casualties.