By Scott Malone

BOSTON (Reuters) - Federal prosecutors on Thursday objected to what they said was a call by lawyers for Boston Marathon bomber Dzhokhar Tsarnaev that jurors "look deep inside" themselves when considering whether they believe the testimony of foreign witnesses.

In a filing in Boston federal court, prosecutors said they objected to what they said was the defense's request that U.S. District Judge George O'Toole instruct the jurors to consider whether they are naturally prejudiced in favor of "people like themselves" and if they tend to discredit the testimony of foreign witnesses.

The jury last week found Tsarnaev, 21, guilty of killing three people and injuring 264 at the April 15, 2013, attack on the marathon and three days later shooting dead a police officer. Next week the jury will begin considering whether to sentence him to death or life in prison without possibility of parole.

Both prosecutors and defense witnesses are set to begin calling another round of witnesses, with the trial's sentencing phase expected to take four weeks before the jury begins deliberations on Tsarnaev's fate.

Thursday's objection by prosecutors was in response to an earlier filing by the defense that, like a great many in Tsarnaev's case, was submitted under seal and barred from public view. The prosecutions' description of the defense filing could not be independently verified.

During the guilt phase of the trial, the jury heard from two foreign nationals, a Chinese exchange student who was friends with one of the three people killed by blast and a Chinese entrepreneur who was carjacked by Tsarnaev and his older brother three days after the bombing.

The lists of witnesses to be called during the sentencing phase have also been filed under seal.

Defense lawyers argued during the trial's first phase that Tsarnaev carried out the bombing not out of his own sense of grievance against the United States but was simply following along in a plot hatched by his 26-year-old brother, Tamerlan.

Tamerlan died following a gunfight with police in the days after the bombing.

(Reporting by Scott Malone; editing by Andrew Hay)