SYDNEY, Feb 11 (Reuters) - Australia’s financial services regulator said it aims to announce new capital rules by the end of this year to make the country’s banks “unquestionably strong”.

The move could add pressure on the country’s major banks as they battle slowing growth and narrowing margins. Investors have heavily sold off bank stocks this year on concerns that onerous capital rules amid slowing growth could hurt earnings.

“As things stand today we should be in a position by the end of the year to set out how an ‘unquestionably strong’ framework will be achieved,” Australian Prudential Regulation Authority (APRA) Chairman Wayne Byres said in a speech published on the regulator’s website on Thursday.

Australia’s four major banks - Commonwealth Bank, Westpac, ANZ Banking Group and National Australia Bank - have together raised A$20 billion ($14.2 billion) since May 2015 as regulators try to make them among the safest in the world.

Their capital ratios are already among the highest in the world, ranging between 13.2 and 14.3 percent, according to their latest filings. ($1 = 1.4086 Australian dollars) (Reporting by Swati Pandey; Editing by Richard Pullin)