Prosecutors allege Lance Cpl. Smith raped a 22-year-old Filipino woman on Nov. 1, while the others -- Lance Cpl. Keith Silkwood, Lance Cpl. Dominic Duplantis and Staff Sgt. Chad Carpentier -- cheered him on.

The rape charges are punishable by up to 40 years in jail. The Marines have refused to answer the charges and the judge entered a plea of innocent for them.

On Monday, U.S. Navy Criminal Investigation Service agent Ronald Veltz testified at the Makati Regional Trial Court that the driver of a van in which the woman was allegedly raped told him the servicemen were indeed with the woman -- identified only as ``Nicole'' -- on that night.

Veltz, a prosecution witness, said that Filipino driver Timoteo Soriano even drew a sketch showing Smith and the woman seated at the back of the van.

Veltz was scheduled to be cross-examined Wednesday and a second Navy investigator was expected to testify, but government prosecutor Emilie Delos Santos said the U.S. Embassy informed them they had no clearance from Washington to allow the investigators to appear.

Embassy officials could not be immediately reached for comment.

It wasn't clear either why Veltz was allowed to testify on Monday.

``They are delaying the proceedings in this case,'' Delos Santos told reporters.

The session adjourned after Judge Benjamin Pozon ordered the embassy to explain why it was invoking diplomatic immunity for Navy investigators.