* FTSE 100 up 0.2 percent
* RBS bucks strong sector trend after results
* IAG gains, operating loss better than consensus
By Tricia Wright
LONDON, Feb 28 (Reuters) - Britain's top shares took a boost on Thursday from assurances from U.S. and European central banks that they would stick with support for their economies, though returning concerns about Italy and the euro zone hung over the market.
The FTSE 100 was up 11.98 points, or 0.2 percent, at 6,337.86 by 0925 GMT. That followed a jump of 0.9 percent in the previous session in the aftermath of a sharp sell-off on Tuesday when Italian elections ended in a stalemate.
U.S. Federal Reserve bank chairman Ben Bernanke sparked a rally on Wall Street on Wednesday after he defended the Fed's asset purchases programme and played down signs of internal divisions. European Central Bank head Mario Draghi issued a similarly dovish set of comments.
"It's reassuring that the Fed are not going to start pulling back QE (quantitative easing) any time soon... but I'm not entirely sure that this rally will continue if the Italian (situation) gets a bit more out of control," Joe Rundle, head of trading at ETX Capital, said.
Stimulus spending by the Fed, alongside the European Central Bank, the Bank of England and others, has underpinned stock markets through a rally stretching back to last July. The FTSE 100 is near five-year highs.
But concerns that the lack of a strong government in Italy will mean it cannot deal with its debt problems, in turn threatening other struggling euro zone borrowers.
Banking stocks notched up solid gains on the central banks' reaffirmation of a dovish stance. Royal Bank of Scotland was the notable exception after disappointing results from the part-nationalised lender.
RBS shed 2.3 percent, among the top FTSE 100 fallers, after the bank made a pretax loss of 5.2 billion pounds, hit by a 4.6 billion charge for losses on the value of its own debt.
"Unfortunately, RBS is starting 2013 in a weaker financial position than the market had anticipated, and if our forecasts for an anaemic RoE recovery - 2 percent in 2013e, 4 percent in 2014e and 6 percent in 2015e - prove to be correct, we believe the shares have further to fall," Investec said in a note.
Investec repeated its "sell" rating on RBS.
Copper miner Kazakhmys was the top faller with a 6.4 percent drop after warning it could be forced to take a hit estimated at over $1.5 billion on the value of its holding in Kazakh rival ENRC.
International Airlines Group, meanwhile, advanced 5.1 percent, topping the blue-chip leader board, after its 2012 operating loss of 68 million euros ($89.14 million) came in better than consensus.
The earnings season has proved mixed so far. Of the 54 percent of STOXX Europe 600 stocks to have posted results, 61 percent have beaten or met forecasts, according to Thomson Reuters Starmine data. (Reporting by Tricia Wright; editing by Patrick Graham)