Stocks mostly traded sideways on Thursday, but the S&P 500 ended its worst week this year as growing pressure on Europe's debt markets revived concerns about the region's financial stability.

The Dow Jones industrial average <.DJI> slipped 14.61 points, or 0.11 percent, to end unofficially at 13,060.14. The Standard & Poor's 500 Index <.SPX> dipped just 0.88 of a point, or 0.06 percent, to finish unofficially at 1,398.08. But the Nasdaq Composite Index <.IXIC> rose 12.41 points, or 0.40 percent, to close unofficially at 3,080.50.

For the week, the Dow fell 1.15 percent, while the S&P 500 lost 0.74 percent in its worst weekly performance since December. The Nasdaq ended the week down 0.36 percent.

The U.S. stock market will be closed on Friday for Good Friday.

(Reporting by Ryan Vlastelica; Editing by Jan Paschal)