Mumbai, July 22 -- The Japanese yen weakened beyond 163 per US dollar on Wednesday, falling to its lowest level since 1986 as rising US Treasury yields and escalating US-Iran tensions boosted demand for the greenback. The currency also remained under pressure from Japan's expanding fiscal spending plans, the Bank of Japan's gradual policy normalization, and a widening interest-rate differential with the US. Meanwhile, Japan's trade balance slipped back into deficit in June as import growth outpaced exports, adding to concerns over the country's external position. Despite the government's Euro11.73 trillion intervention earlier this year, the yen continues to trade near its weakest level in four decades, with markets closely watching for a...