RBS said its customers were reporting that services were coming back on line after the bank's online and debit card payments failed Monday evening.
The British bank apologized to its customers and said it would confirm when all systems return to normal service.
"If customers have been left out of pocket as a result of these system problems, we will put this right," said RBS in a statement.
Millions of customers across the United Kingdom were unable to withdraw cash, pay for goods or use telephone and online banking services as RBS and its retail banking unit Netwest's online systems and debit cards failed on Monday evening.
The bank's Irish unit, Ulster Bank, also reportedly faced similar technology glitches.
RBS, which is 82 percent owned by the UK government, faced a probe by the Financial Conduct Authority in April when technology failure left customers unable to avail the bank's card and online services.
A software upgrade gone wrong also led to similar problems for RBS' customers in June 2012.
(Reporting by Aashika Jain in Bangalore; Editing by Leslie Gevirtz, Bernard Orr)