By John Geddie

LONDON, July 24 (Reuters) - Euro zone bond yields fell on Friday after surveys showed slowing private sector growth in the bloc's biggest economy, keeping the pressure on the European Central Bank to stimulate the euro zone's fragile recovery.

Investors were poised for disappointment after a sharper than expected drop in euro zone consumer confidence data on Thursday, and a survey showing China's factory sector contracted by the most in 15 months.

Analysts said the weak data run is a bad omen for next week's euro zone inflation print, all of which conspires to up the ante on the ECB to supercharge its bond-buying quantitative easing scheme.

"We should keep in mind that the ECB has quite optimistic growth assumptions underlying their QE scheme," said Commerzbank analyst Michael Leister.

"So if we get a comprehensive set of disappointing data it will increase the expectation that the ECB will have to keep QE longer or increase the monthly size."

Germany's private sector grew at a slightly slower rate in July than in the previous month, which also led to weaker-than-expected euro area data.

Markit's flash composite Purchasing Managers' Index (PMI) tracking manufacturing and services activity which accounts for more than two-thirds of the German economy inched down to 53.4 from 53.7 in June.

Top-rated German bond yields -- the bloc's benchmark -- fell 3 basis points to a three-week low of 0.67 percent , as did riskier bonds in the bloc's southern periphery.

Under normal circumstances, weak data would prompt investors to cut risk and take refuge in safe haven bonds but the prospect of more central bank stimulus has altered trading strategies.

Portuguese, Spanish and Italian yields were also down 3-5 bps at 2.60 percent, 1.88 percent and 1.94 percent.

Irish bonds were some of the best performers in early European trading, with yields down 4 bps at 1.34 percent after its debt agency said on Thursday it may ease its funding requirements from 2018 to 2020 via bond buy-backs and switches.

"By extending maturity, Ireland has improved its fundamentals and if the Irish curve is smoother then there may more interest in their bonds from relative value investors, so overall this is a smart move from the NTMA (debt agency)," said Mizuho strategist Peter Chatwell.

Greece was the only country in the euro zone to see yields rise on Friday, climbing 10 bps to 11.57 percent.

Athens does not yet qualify for the ECB's QE scheme, but even when it does, purchases will likely be too small to push the country's borrowing costs low enough to regain market access soon.