The African and Eurasian desert belt is primarily formed due to its location in the sub-tropical high-pressure cells. These high-pressure areas are characterised by descending air, which is dry and leads to arid conditions, forming deserts.

However, the influence of warm ocean currents is not a significant factor in the formation of these desert belts. Warm ocean currents generally increase the moisture content in the air, leading to more precipitation, not desert conditions.

Therefore, the correct answer is that the desert belt is located in the sub-tropical high-pressure cells.