* UK banks' Iberian exposure is "relatively little" - FSA
* FSA says exposure to Ireland is "not worrying"
* RBS shares up 0.1 percent, Lloyds down 0.4 percent
(Adds further comments on Portugal, Spain, background)
LONDON, Nov 23 (Reuters) - Britain's Financial Services Authority (FSA) regulator sought on Tuesday to reassure investors that the exposure of UK banks to struggling euro zone economies such as Ireland is not a cause for undue concern.
Shares in part-nationalised UK banks Royal Bank of Scotland and Lloyds have fallen sharply in recent weeks on worries over their exposure to Ireland, which has called for international aid to fix its economic problems.
However, FSA Chairman Adair Turner told parliament's Treasury Committee that British banks were not "worryingly" exposed to Irish banks or Irish government bonds.
The exposure to Irish bonds was "not at all worrying in their scale," Turner told British lawmakers.
"Nor indeed is direct exposure of UK banks to Irish banks out of line with what you would expect," added Turner.
Britain's main exposure was to the Irish economy since two banks, RBS and Lloyds' HBOS unit, have significant business in Ireland, he added.
Many analysts and investors have highlighted Portugal and Spain as future weak spots in the euro zone economy, but the FSA said that the exposure of British banks to those countries was relatively small and not on the same scale as to Ireland.
"In both of those (Portugal and Spain), we again have relatively little exposure to sovereign bonds," said Turner.
The Bank for International Settlements said earlier this year that British banks had an exposure at the end of March of $142 billion to Spain, $32 billion to Portugal and $222 billion to Ireland.
RBS shares were up 0.3 percent by 1220 GMT, after falling 5 percent on Monday, while Lloyds shares slipped 0.8 percent.