Asahi newspaper reported that Japan's Fair Trade Commission is worried about a BHP Billiton takeover of Rio Tinto and has begun talks with counterparts in Europe and Australia about a possible investigation.

The Asahi newspaper said the Japanese watchdog was likely to talk with counterparts in South Korea and Taiwan, countries which also have steelmakers highly dependent on the miners.

Japan's Iron and Steel Federation, which represents companies such as Nippon Steel Corp and JFE Steel Corp had earlier said that it vehemently opposes the proposed merger, arguing that it would be anti-competitive.