Armando Lopez-Lopez challenges the sentence imposed by the district court * after Lopez-Lopez pleaded guilty to drug-conspiracy and money-laundering charges. Counsel has filed a brief and moved to withdraw under Anders v. California) 386 U.S. 738, 87 S.Ct. 1396, 18 L.Ed.2d 493 (1967). Although we granted Lopez-Lopez permission to file a pro se supplemental brief, he has not done so.

Counsel argues that the district court committed error by increasing Lopez-Lopez’s base offense level for possession of a dangerous weapon. We disagree. In our view, the district court correctly applied the enhancement in light of a witness’s testimony that Lopez-Lopez held up his gun and warned her, “[Y]ou know what we do to narcas.” See U.S.S.G. § 2D1.1, comment. (n.3) (adjustment should be applied if weapon was present, unless it is clearly improbable weapon was connected with offense); United States v. Behler, 187 F.3d 772, 777 (8th Cir. 1999) (district court’s assessment of credibility is “virtually unre-viewable”; clear-error standard).

Having reviewed the record independently in accordance with Penson v. Ohio, 488 U.S. 75,109 S.Ct. 346, 102 L.Ed.2d 300 (1988), we find no other nonfrivolous issues. Thus, we grant counsel’s motion to withdraw, deny as moot Lopez-Lopez’s motion for appointment of appellate counsel, and affirm the district court.