The U.S. dollar struggled to build on an overnight rebound from three-month lows as investors assessed expanded Iran-related sanctions and efforts to reduce pressure on longer-dated Treasury yields. The euro edged up to $1.1668, near a three-month peak reached the previous week, while sterling rose 0.1% to $1.3639, close to a six-month high. U.S. Treasury Secretary Scott Bessent said countries should cut business ties with Iran or risk losing access to the dollar-based financial system, a warning that could encourage affected parties to acquire dollars before sanctions take effect. The Canadian dollar was flat at $1.3844 after falling 0.6% in the prior session amid a U.S. threat to raise tariffs on Canadian goods following the collapse of trade negotiations. The yen strengthened slightly to 159.21 per dollar, remaining well above its multi-decade low of about 164 after giving back most of its intervention-related gains. The dollar index, which tracks the U.S. currency against six major peers, slipped to 98.96 in Asian trading after rising 0.16% overnight. The Australian and New Zealand dollars each gained 0.1% ahead of the Reserve Bank of Australia's August policy meeting minutes, trading at $0.7157 and $0.5965, respectively. Bitcoin rose 1% to $78,817.34 after recording its biggest weekly gain in nearly 3-1/2 years the previous week. Treasuries received limited support after a report said the U.S. Treasury could use part of its cash balance to buy longer-dated bonds and reduce borrowing costs. The 2-year Treasury yield was unchanged at 4.246%, while the 10-year yield stood at 4.704%. Investors are awaiting Federal Reserve Chair Kevin Warsh's debut speech in Jackson Hole, Wyoming, on Friday for signals on the recent increase in bond yields and his independence from the Trump administration. Analysts said policy uncertainty is limiting the scope for further dollar gains.