Japan's Nippon Steel & Sumitomo Metal Corp will press hard to approve a capital increase for Brazilian steelmaker Usiminas SA this week, with a threat to sue if fellow shareholders block the motion, a source with knowledge of the matter said on Tuesday. The Japanese group will propose a cash injection of 1 billion reais at a Friday board meeting, and is willing to finance the capital increase alone if the other major shareholder, Italian-Argentinian conglomerate Techint Group, refuses to participate, the same source said.