MANHATTAN - ? Authorities are continuing stepped up security in NYC following a 'credible' terror threat from al-Qaida.

Sources say uniformed and undercover police officers will ride the LIRR today.Yesterday, K-9 units sniffed out vehicles on bridges and tunnels. In addition, armed guards from at least eight law enforcement agencies greeted commuters at the city?s train stations. Security still tight after 9/11 memorial services