The FTSE 100 <.FTSE> index is seen opening down 54-55 points, or 1 percent on Thursday, according to financial bookmakers, tracking market falls in Asia as leaders of the world's biggest economies gather in France for a G20 summit set to be dominated by the threat of Greece falling out of the euro zone.

The leaders of France and Germany, angered at Greece's shock move to call a referendum on its latest bail-out plan negotiated last week, told Prime Minister George Papandreou on Wednesday that Athens would not receive another cent in EU aid until it decides whether it wants to stay in the euro zone.

The blue chip index closed up 62.53 points, or 1.1 percent on Wednesday at 5,484.10, recovering after two sessions of hefty falls, fuelled by a bounce back by commodity issues, and buoyed by earnings news and U.S. data.

U.S. blue chips <.DDI> gained 1.5 percent on Wednesday, led by a rally in financial stocks, but Asian equities fell back on Thursday, and U.S. stock futures were also lower, as fears that Europe's debt crisis could unleash financial chaos prompted investors to shed riskier assets.

As well as watching events at the G20 summit in Cannes, investors were also focussed on Frankfurt, where the European Central Bank will hold its first policy meeting under new President Mario Draghi.

Many analysts see the ECB as the only institution with the firepower to calm the euro zone crisis, and the key question after the meeting -- at which no change in interest rates is expected -- will be whether it will increase its purchases of bonds issued by debt-ridden euro zone states.

On Wednesday the U.S. Federal Reserve offered no new stimulus, but said it was mulling the possibility of buying more mortgage debt to spur a struggling recovery.

On the domestic macroeconomic front, October's UK Markit/CIPS services PMI report, due at 9:28 a.m., is forecast to show a reading of 52.0, down from 52.9 in September.

Across the Atlantic, U.S. initial weekly jobless claims will be released at 1:30 p.m., with October's non-manufacturing ISM index, and revised September durable goods orders due at 3 p.m.

(Reporting by Jon Hopkins; Editing by Greg Mahlich)