Daniel Lugo-Sanchez challenges the 120-month statutory minimum sentence the district court 1 imposed after he pleaded guilty to a drug charge. His counsel has moved to withdraw and filed a brief under Anders v. California, 386 U.S. 738, 87 S.Ct. 1396, 18 L.Ed.2d 493 (1967), arguing that Lugo-Sanchez’s plea was involuntary because he was led to believe he would be eligible for safety-valve relief pursuant to 18 U.S.C. § 3553(f). LugoSanchez has filed a pro se supplemental brief arguing that his plea was “coerced” because his attorney told him that he would receive a 5-year sentence, and he did not understand the legal terms used in the proceedings; that he should have been given a more lenient sentence under U.S.S.G. § 5K2.13 due to his mental deficiencies; that his criminal record does not justify the severity of his sentence; and that his sentence was affected by Blakely v. Washington, 542 U.S. 296, 124 S.Ct. 2531, 159 L.Ed.2d 403 (2004), and United States v. Booker, 543 U.S. 220, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005). We reject each of these arguments and affirm.

*687 Initially, we note that the involuntary-guilty-plea claim is not properly before us, as Lugo-Sanchez did not present the claim to the district court, and in fact his attorney specifically confirmed that LugoSanchez was prepared to proceed with sentencing after being informed of his ineligibility for safety-valve relief. See United States v. Murphy, 899 F.2d 714, 716 (8th Cir. 1990) (claim of involuntary guilty plea must first be presented to district court, and is not cognizable on direct appeal). 2

Further, Lugo-Sanchez’s intellectual functioning is not a basis for a sentence below the mandatory minimum, see 18 U.S.C. § 3553(e), (f); any ineffective-assistance claim should be raised in 28 U.S.C. § 2255 proceedings, see United States v. Hughes, 330 F.3d 1068, 1069 (8th Cir. 2003); and there was no error under Blakely or Booker, as Lugo-Sanchez was sentenced to the statutory mandatory minimum, see United States v. Torres, 409 F.3d 1000,1004 (8th Cir. 2005).

Having reviewed the record independently under Penson v. Ohio, 488 U.S. 75, 109 S.Ct. 346, 102 L.Ed.2d 300 (1988), we have found no nonfrivolous issues. Accordingly, we affirm, and we grant counsel’s motion to withdraw.