(ShareCast News) - Royal Bank of Scotland has agreed to pay £88.4m to settle claims by a US regulator that it sold toxic mortgage-backed securities to now-defunct credit unions, according to a court filing on Tuesday.The National Credit Union Administration, which regulates, charters and supervises federal credit unions, filed a federal lawsuit in in 2013 on behalf of Southwest Corporate and Members United Corporate.The NCUA has brought a number of lawsuits against banking defendants over securities sold to several credit unions that failed during the financial crisis.In the case of RBS, it claimed the bank ignored underwriting guidelines for the securities, which were rated triple-A when they were bought by the credit unions for more than $300m before the credit crisis.At 1023 BST, RBS shares were up 0.2% at 329.60p.