A three-day conference on African development wrapped up Friday in Yokohama by adopting a 13-page joint declaration with 53 African countries touting Japan's strategic policy shift from government aid to promoting private-sector investment.

But the policy papers and remarks by Japanese officials suggested Tokyo was pursing an unofficial agenda at the Tokyo International Conference on African Development: how to differentiate Japan's economic cooperation from that of China, which has long surpassed Japan as a massive business investor in the continent's rapidly growing economies.

The Yokohama Declaration drafted by Japan called for "quality infrastructure investment," which experts say is a veiled criticism of Beijing infrastructure projects that often come with high-interest loans and are criticized as "debt-trap diplomacy."