Stress in the banking sector is being closely monitored for its potential to trigger a credit crunch, a U.S. Federal Reserve policymaker said on Sunday, as a European Central Bank official also flagged a possible tightening in lending. Authorities around the world are on high alert for the fallout from recent turmoil at banks following the collapse in the United States of Silicon Valley Bank (SVB) and Signature Bank and the rescue takeover a week ago of Credit Suisse.