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* FTSE 100 up 0.5%, FTSE 250 up 0.4%
* Oil majors biggest support as crude prices jump
* Dixons Carphone slumps after poor results
* Dunelm gains after forecast upgrade
June 20 (Reuters) - London's FTSE 100 rebounded Thursday on strong gains in oil majors and miners as investors were encouraged by the U.S. Federal Reserve's stance on potential rate cuts, while electronics retailer Dixons Carphone tanked.
The FTSE 100 index was up 0.5% and the FTSE midcap index rose 0.4% by 0707 GMT.
The U.S. Federal Reserve kept interest rates unchanged on Wednesday and signalled rate cuts could start as early as July, offering respite to investors who have been uneasy about by weak economic data and global trade tensions.
FTSE 100 component Fresnillo surged nearly 7%, its biggest one-day gain in eight months, as gold prices hit their highest in more than five years after the Fed statement pressured the dollar.
Among midcaps, Dixons Carphone plunged 23.5% after it warned of a big drop in profit for the current year while reporting a slump in full-year profit as it struggles with a fierce mobile phone market.
Homewares retailer Dunelm climbed 4.3% after it raised its annual earnings target for the second time in just over two months, capping off a year in which it saw a surge in online orders. (Reporting by Muvija M in Bengaluru; Editing by Bernard Orr)