U.S. stocks closed out a difficult week on a modestly lower note Friday, as investors continued to monitor Britain’s frenzied debate on whether to leave the European Union. The debate took on a new level of concern after the killing of a member of parliament.

Technology stocks were among the biggest decliners. Apple fell as a patent dispute in China threatened to jeopardize futures sales of iPhones in the world’s second-largest economy.

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The Dow Jones industrial average lost 57.94 points, or 0.3 percent, to 17,675.16. The Standard & Poor’s 500 index fell 6.77 points, or 0.3 percent, to 2,071.22 and the Nasdaq composite fell 44.58 points, or 0.9 percent, to 4,800.34.

Anxiety over the British referendum coming up next Thursday continued to dominate trading. Stocks have fallen six out of the past seven trading days. This week the Dow and S&P 500 each lost 1 percent while the Nasdaq gave up almost 2 percent.

Investors interpreted the assassination of a well-regarded British politician as something that could sway more voters to stay in the EU. U.K. and European stocks and the British pound rose against the euro and dollar. The pound rose to $1.4375 compared with $1.4205 the day before.