By Carla Mozee, MarketWatch

LONDON (MarketWatch) -- European stocks fell Monday, facing a third day of losses as geopolitical tensions between Russia and Ukraine weighed on sentiment, but a change in leadership at Tesco PLC lifted shares of the British grocer.

The Stoxx Europe 600 index fell 0.3% to 338.81. Investors appeared cautious as leaders in Europe called for sharper sanctions against Russia, saying Moscow hasn't done enough to resolve its conflict with Kiev.

Russian stocks slumped for a sixth day on the tensions, with the MICEX Index droppung 1.3%.

Russia has also been under criticism for its role in handling an investigation into the downing of a Malaysia Airlines plane last week, which killed nearly 300 passengers and crew members.

In other trading action, shares of Banco Espírito Santo fell 1.7% in the wake of Friday's filing for creditor protection by its parent company, Portuguese conglomerate Espírito Santo International SA.

But shares of Tesco PLC outperformed the broader market, rising 3.1% after the U.K. grocer named a new chief executive officer, as it warned of difficult trading conditions. Dave Lewis will join Tesco on Oct. 1, succeeding Philip Clarke, who will exit the board, but continue to support the transition until January 2015. Shares of rival grocer Wm Morrison Supermarkets PLC fell 2%.

Tesco said current trading conditions are "more challenging than we anticipated" in its first-quarter interim statement released June 4. Lewis currently serves as president of Unilever PLC's personal care unit. Unilever shares were off 0.1%.

Among national markets, the U.K.'s FTSE 100 index fell 0.4% to 6,724, and France's CAC 40 index lost 0.6% to 4,309.56. Germany's DAX 30 index fell 0.9% to 9,633.

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