We study oscillations of an electric current-carrying and axially-symmetric string loop in the vicinity of a Schwarzschild black hole embedded in an asymptotically uniform magnetic field. The radial profiles of frequencies of small oscillations of the string loop around stable equilibrium points are given for the radial and vertical harmonic modes that are relevant also in the quasi-periodic stages of the oscillations. Their properties in dependence on the uniform magnetic field intensity and angular momentum parameters of the string loops are determined. We examine the relevance of resonant phenomena of the radial and vertical string-loop oscillations at their frequency ratio 3 : 2. The oscillatory frequencies of the string loops are compared with thefrequencies of high-frequency quasi-periodic oscillations (HF QPOs) observed in the microquasars GRS 1915+105, XTE 1550-564, GRO 1655-40 containing a black hole. We have demonstrated that the influence of the uniform magnetic field does