European shares extend losses on Greek concerns

* Pan-European FTSEurofirst 300 index falls 0.3 pct

* Greek shares down 2.1 pct, Greek banks fall 4.3 pct

* Hennes & Mauritz slips after warning on dollar

By Atul Prakash

LONDON, June 25 (Reuters) - European shares extended losses on Thursday as concerns that Greece could be edging closer to a debt default prompted investors to cut their exposure to risk.

As a deadline for a deal draws near, euro zone finance ministers accused Athens of refusing to compromise, while a senior official of Greece's ruling Syriza party dismissed reform proposals from creditors as "blackmail".

EU leaders will hold a summit on the Greek crisis in Brussels on Thursday.

"Hopes of a quick resolution for Greece seem to be fading," Philippe Gijsels, head of research at BNP Paribas Fortis Global Markets, said. "Where a quick deal seemed to be within reach only a couple of days ago, talks once again seem to be stuck."

Greece's benchmark ATG share index fell 2.1 percent. The country's banking index dropped 4.3 percent, with National Bank (NYSE: NBHC - news) of Greece, Alpha Bank (Other OTC: ALBWF - news) and Bank of Piraeus falling 3.5 to 5.3 percent.

"There is still a bit of optimism left that a deal can be done ...A failure to reach a deal is certainly not priced into the market just yet," Markus Huber, senior analyst at Peregrine & Black, said in a note.

At 0739 GMT, the pan-European FTSEurofirst 300 index was down 0.3 percent at 1,572.06 points after closing 0.4 percent lower in the previous session.

The index hit a three-week high on Tuesday on expectations that Greece and its international creditors were close to finalising an agreement. The index has since retreated 1.6 percent as negotiations hit further snags.

Among other movers, the world's second-biggest fashion retailer Hennes & Mauritz fell 2.2 percent after saying a stronger dollar would result in gradually increased purchasing costs when sourcing for the coming quarters of 2015.

Europe bourses in 2015: http://link.reuters.com/pap87v

Asset performance in 2015: http://link.reuters.com/gap87v

Today's European research round-up (editing by John Stonestreet)