By Christoph Steitz and Nina Chestney

FRANKFURT/LONDON (Reuters) -Russia resumed pumping gas via its biggest pipeline to Europe on Thursday after a 10-day outage, allaying some of Europe's immediate supply fears but not enough to end the threat of rationing to cope with potential winter shortages.

Supplies via Nord Stream 1, which runs under the Baltic Sea to Germany, were halted for maintenance on July 11 but, even before that outage, flows had been cut to 40% of the pipeline's capacity in a dispute sparked by Russia's invasion of Ukraine.

Thursday's flows were back at that 40% capacity level, Nord Stream figures showed, a day after Russian President Vladimir Putin warned that supplies could be cut further or even stop.

The resumption of Nord Stream supplies at levels that remain well below the pipeline's capacity means Germany, which is particularly reliant on Russian fuel, and other European economies are still struggling to find enough gas for winter.

"In view of the missing 60% and the political instability, there is no reason yet to give the all-clear," German network regulator president Klaus Mueller wrote on Twitter.

Gas flows via other pipeline routes, such as Ukraine, have also fallen since Russia invaded its neighbour in February, in what Moscow calls a "special military operation".

Germany and several other states have already activated the first stages of emergency plans that in some cases could lead to rationing. Greece said on Thursday it would implement rotating power cuts as a last resort if necessary.

The EU aims to have gas storage facilities across the bloc 80% full by Nov. 1. Inventories are now about two-thirds full, with a slowing pace of refilling. https://tmsnrt.rs/3Ba2N2O

At current reduced flow rates, the German network regulator said Germany would struggle to reach its own target, which it said on Thursday it was raising to 95% by Nov. 1. Berlin said it would introduce other measures to save gas.

"Further disruptions are expected as Russia seeks to increase political and economic pressure on Europe as winter approaches," Wood Mackenzie analyst Penny Leake said.

Gazprom, which has a monopoly on Russian gas exports by pipeline, did not respond to a request for comment.

EMERGENCY STEPS

To try to prevent a winter supply crunch, the European Commission has proposed a voluntary target for all EU states to cut gas use by 15% from August to March compared to usage in same period of 2016-2021. The Commission proposal would enable Brussels to make the target mandatory in a supply emergency.