Public transport agencies in big US cities are seeking help from the government to avoid default and billions of dollars of payments on leasing contracts that have soured amid problems at AIG and monoline bond insurers.

More than 30 transit authorities in 17 states are at risk of default, according to a letter to the US Treasury and the Federal Reserve from leaders of the congressional transportation committee. The letter says that up to $4bn (€3.1bn, £2.5bn) of deals are immediately at risk.