* Pan-European FTSEurofirst 300 closes down 0.3 pct
* Greek shares end day flat
* Endesa up after report of private-equity interest
* Hennes & Mauritz slips after warning on dollar (Updates with closing prices)
By Atul Prakash and Lionel Laurent
LONDON, June 25 (Reuters) - European shares closed lower on Thursday as Greece failed again to clinch a deal with its international creditors, setting up a last-ditch effort on Saturday to avert a default.
The pan-European FTSEurofirst 300 index closed down 0.3 percent at 1,573.05 points, while the euro zone's EuroStoxx 50 ended the day flat.
Telecoms stocks gained on expectations of more deals after Vivendi increased its stake in Telecom Italia .
Greek markets edged up, with traders citing growing optimism for some kind of deal despite grinding uncertainty over the outcome of the talks in Brussels and varying opinions on whether the markets expect a Greek default.
Peregrine & Black senior analyst Markus Huber said: "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."
Greece's benchmark ATG share index rose 0.1 percent. The country's banking index slipped 0.6 percent.
Some fund managers said European equities remained attractive regardless of the back-and-forth surrounding Greece.
"Forget Greece, buy Europe," BCS Asset Management portfolio manager Edmund Shing said. "The macro outlook is pretty damn good for Europe ... I expect a bunch of (company) earnings upgrades to come through."
Among standouts, shares in Endesa were up 1.9 percent after Reuters reported private-equity funds CVC and KKR were studying a bid for a "meaningful" stake in the Spanish unit of Italy's Enel.
And the world's No. 2 fashion retailer Hennes & Mauritz fell 3 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: link.reuters.com/pap87v
Asset performance in 2015: link.reuters.com/gap87v
Today's European research round-up (Editing by Catherine Evans)