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* Vodafone jumps as Iliad offers to merge Italian units

* Entain gains on Jefferies upgrade

* FTSE 100 rises 0.4%, FTSE 250 up 0.2%

Dec 18 (Reuters) - The UK's FTSE 100 advanced on Monday as heavyweight energy stocks rose, tracking strength in crude oil prices, while Vodafone's shares topped the index after telecom firm Iliad submitted a proposal to create a joint venture in Italy.

The blue-chip FTSE 100 gained 0.4% as of 0926 GMT, while the more domestically-focussed FTSE 250 mid-cap index also gained 0.2%.

Vodafone jumped 6.2% after Iliad said it submitted a proposal to the telecom company to merge their Italian businesses.

Heavyweight energy stocks added 0.8%, tracking a jump in crude oil prices.

On the downside, precious metal miners fell 1.3% as Fresnillo lost 7.1% after Morgan Stanley downgraded its rating to "underweight" from "equal-weight".

Looking ahead, data due this week includes inflation readings in the UK, euro zone, and the U.S., along with GDP estimates from Britain and the U.S.

The FTSE 100 is extending three consecutive weeks of gains, which came on the back of hopes that the U.S. Federal Reserve could consider cutting interest rates soon.

Tempering some of those expectations, Atlanta Fed President Raphael Bostic pushed back late on Friday saying the U.S. central bank can begin reducing interest rates "sometime in the third quarter" of 2024 if inflation falls as expected.

His comments came after New York Fed President John Williams also pushed back against rate-cut expectations in an interview on Friday.

"That burst a few traders' bubbles, coming after a week that saw U.S. bond yields tumbling in anticipation of rate cuts in 2024," said Steve Clayton, head of equity funds at Hargreaves Lansdown.

Among other individual stocks, GSK gained 1.2% after the drugmaker said its cancer drug combination met its primary goal in a late-stage trial.

Entain advanced 5.6% after Jefferies upgraded the sports betting firm's rating to "buy" from "hold".

(Reporting by Shashwat Chauhan in Bengaluru; Editing by Sonia Cheema and Janane Venkatraman)