Asian shares began the week on a cautious note on Monday as investors braced for a possible escalation in East-West tensions after anti-Kiev rebels declared victory in a referendum on self-rule in eastern Ukraine. Western leaders have threatened more sanctions in the key areas of energy, financial services and engineering if Moscow disrupts a presidential election planned in Ukraine on May 25. MSCI’s broadest index of Asia-Pacific shares outside Japan ticked down 0.1 percent while Japan’s Nikkei share average was almost flat. Oil prices rose slightly on concerns about Ukraine, with U.S.