As relentless Russian airstrikes and missile barrages continue to pummel Ukrainian cities, leaving a rising trail of death and civilian suffering, a new diplomatic rift has emerged over a U.S. decision to extend a key exemption to Western sanctions on Russian crude oil exports. The U.S. move extends the window for global buyers to purchase Russian oil and petroleum products already loaded onto cargo vessels at sea until May 16, a measure Washington says is designed to head off a catastrophic global energy supply crunch stoked by escalating conflict between the U.S., Israel and Iran.