BOSTON (Reuters) - Surveillance video showing a black Muslim man being shot and killed in Boston by law enforcement officers attempting to question him in a terrorism investigation will not be released until after his funeral, prosecutors said on Friday.

The Suffolk County District Attorney has vowed a full investigation into an incident on Tuesday in which Usamaah Abdullah Rahim was fatally shot by a Boston police officer and an FBI agent who had approached him in a parking lot, after Rahim, a 26-year-old security guard, allegedly threatened them with a large knife.

Members of the Rahim family late on Thursday met with Suffolk County District Attorney Daniel Conley and viewed the video, which police have said shows officers ordering Rahim to drop a weapon and initially retreating before going on to open fire.

The video will not be released until after Rahim's funeral, a spokesman for Conley said. Rahim was due to be buried on Friday, local media reported.

With police shootings of blacks sparking riots and mass protests across the country over the past year, officials want to release the video quickly to stifle potential unrest and squelch rumors on social media that Rahim was shot from behind.

Rahim had been under 24-hour-a-day surveillance by the Joint Terrorism Task Force when a wiretap revealed early on Tuesday that he planned to attempt to behead police officers around Boston, according to an FBI affidavit filed in Boston federal court on Wednesday.

Rahim and two associates had spoken in the same sort of code that Islamic militants use, the affidavit alleged.

An attorney flanked by members of the Rahim family told reporters on Thursday that they had seen no evidence that he had adopted militant or extremist views.

(Reporting by Scott Malone; Editing by Alan Crosby)