diff --git a/internal/context/context.go b/internal/context/context.go
index ad9a08d..cef8857 100644
--- a/internal/context/context.go
+++ b/internal/context/context.go
@@ -120,6 +120,26 @@ func AddAusfUeContextToPool(ausfUeContext *AusfUeContext) {
 	ausfContext.UePool.Store(ausfUeContext.Supi, ausfUeContext)
 }
 
+func AddAusfUeContextToPoolIfNoOngoing(ausfUeContext *AusfUeContext) (existing *AusfUeContext, ok bool) {
+	for {
+		// TODO: model ServingNetworkName in the context key/lookup lifecycle if
+		// AUSF needs to separate the same SUPI across serving networks.
+		context, loaded := ausfContext.UePool.LoadOrStore(ausfUeContext.Supi, ausfUeContext)
+		if !loaded {
+			return nil, true
+		}
+
+		existingContext := context.(*AusfUeContext)
+		if existingContext.AuthStatus == models.AusfUeAuthenticationAuthResult_ONGOING {
+			return existingContext, false
+		}
+
+		if ausfContext.UePool.CompareAndSwap(ausfUeContext.Supi, existingContext, ausfUeContext) {
+			return existingContext, true
+		}
+	}
+}
+
 func CheckIfAusfUeContextExists(ref string) bool {
 	_, ok := ausfContext.UePool.Load(ref)
 	return ok
diff --git a/internal/sbi/processor/ue_authentication.go b/internal/sbi/processor/ue_authentication.go
index e519dbc..57b5815 100644
--- a/internal/sbi/processor/ue_authentication.go
+++ b/internal/sbi/processor/ue_authentication.go
@@ -360,7 +360,21 @@ func (p *Processor) UeAuthPostRequestProcedure(c *gin.Context, updateAuthenticat
 	ausfUeContext.ServingNetworkName = snName
 	ausfUeContext.AuthStatus = models.AusfUeAuthenticationAuthResult_ONGOING
 	ausfUeContext.UdmUeauUrl = udmUrl
-	ausf_context.AddAusfUeContextToPool(ausfUeContext)
+	if updateAuthenticationInfo.ResynchronizationInfo != nil {
+		ausf_context.AddAusfUeContextToPool(ausfUeContext)
+	} else if existingContext, ok := ausf_context.AddAusfUeContextToPoolIfNoOngoing(ausfUeContext); !ok {
+		logger.UeAuthLog.Warnf("authentication already in progress for SUPI %s with status %s",
+			ueid, existingContext.AuthStatus)
+		problemDetails := models.ProblemDetails{
+			Title:  "Authentication already in progress",
+			Cause:  "AUTHENTICATION_IN_PROGRESS",
+			Detail: "an authentication procedure for this SUPI is already in progress",
+			Status: http.StatusConflict,
+		}
+		c.Set(sbi.IN_PB_DETAILS_CTX_STR, problemDetails.Cause)
+		c.JSON(http.StatusConflict, problemDetails)
+		return
+	}
 
 	logger.UeAuthLog.Infof("Add SuciSupiPair (%s, %s) to map.\n", supiOrSuci, ueid)
 	ausf_context.AddSuciSupiPairToMap(supiOrSuci, ueid)