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In initial trade, the British capital's benchmark FTSE 100 index was down 0.1 percent at 7,518.04 points.
In the eurozone, Frankfurt's DAX 30 index shed 0.4 percent to 12,768.46 points, while the Paris CAC 40 declined 0.5 percent to 5,280.20 compared with the closing level on Monday.
Asian stocks struggled Tuesday as investors nervously await key political events later in the week, such as the testimony before the US Congress of President Donald Trump's former FBI chief.