TORONTO, April 24 (Reuters) - Canada's main stock index fell on Tuesday as lower oil prices weighed on energy shares, while investors worried about the prospect of higher global borrowing costs after the benchmark U.S. 10-year Treasury note yield hit 3 percent for the first time in four years. * The Toronto Stock Exchange's S&P/TSX composite index closed down 75.06 points, or 0.48 percent, at 15,477.00. It touched its highest intraday since March 21 at 15,589.20. * The energy group fell 0.6 percent as oil prices declined. * U.S. crude oil futures settled 1.4 percent lower at $67.70 a barrel as concerns faded over the possibility that the United States might reinstate sanctions against Iran. * The rise in Treasury yields reflected the durability of the U.S. economic expansion and stoked views the three-decade-old bull market in bonds is coming to an end. * Eight of the index's 10 main groups ended lower. Industrials fell 0.6 percent as shares of railroad companies lost ground. * The largest decliner was PrairieSky Royal Ltd , down 7.5 percent, after it reported first-quarter results after the bell on Monday. * The largest percentage gainer on the TSX was Mitel Networks Corp , which rose 9.6 percent. The telecommunications gear maker says it is selling itself to an investor group led by Searchlight Capital Partners for about $2 billion. * Restaurant Brands International Inc rose 4.3 percent to C$72.04 after the company reported first-quarter profit that topped estimates. The company and its franchisees will spend C$700 million over four years to revamp coffee chain Tim Hortons following a round of bad publicity over its management of the Canadian chain. * The TSX posted 10 new 52-week highs and five new lows. (Reporting by Fergal Smith Editing by James Dalgleish)