U.S. stocks ended the week on a low as a deepening economic crisis in Turkey dragged on bank stocks and triggered fears that it could spread to other global economies.

A slump in the Turkish lira worsened after President Donald Trump doubled tariffs on steel and aluminum imported from the country.

David Miller, chief investment officer at Catalyst Funds: (SOUNDBITE) (English) CHIEF INVESTMENT OFFICER AT CATALYST FUNDS, DAVID MILLER, SAYING: "Well the Turkish lira is taking a really big hit today as has the Turkish stock market.

U.S. markets are taking a bit of a hit, but the place where you're really seeing the hit is on emerging markets, China, Turkey for sure, Russia, they're all really taking it on the chin today with these new tariffs." A drop in technology shares added to the bearish tone.

The S&P technology index fell, with Intel down after Goldman Sachs downgraded the stock to "sell." Microchip Technology shares fell close to 11 percent after a disappointing second-quarter revenue forecast.

Citigroup, JPMorgan, Wells Fargo and Bank of America were also lower.

Shares of trade-sensitive companies also declined, including Boeing, 3M and Caterpillar.

Reverberations spread through global markets, with Europe especially hit as investors took fright over bank exposures to Turkey.