NEW YORK -- Investors in U.S.-based mutual funds pulled $968 million out of stock funds in the week ended March 19 on tensions over Ukraine and a shift in outlook for U.S. monetary policy, data from the Investment Company Institute showed on Wednesday.

The outflows in the week ended last Wednesday marked the biggest withdrawals from stock funds since October 2013 and the first outflows since December, according to data from ICI, a U.S. mutual fund trade organization.

The net outflow followed inflows of $4.22 billion over the previous week.

Funds that specialize in U.S. stocks posted outflows of $3.8 billion, marking their biggest outflows since early December. Funds that mainly hold non-U.S. stocks still attracted $2.8 billion, up from an inflow of $2.3 billion over the prior week.

The benchmark Standard & Poor's 500 stock index fell 0.4 percent over the weekly period on East-West tensions surrounding Ukraine and in the wake of comments from Federal Reserve Chair Janet Yellen on the possibility that U.S. interest rates could be hiked earlier than expected.

Bond funds attracted $2.5 billion in new cash, marking their sixth straight week of inflows. The weekly inflow streak into bond funds has marked a recovery in demand after fears of a pullback in the Fed's bond-buying program spurred record outflows of $83.4 billion from the funds last year, according to ICI data.

Hybrid funds, which can invest in stocks and fixed-income securities, attracted $1.8 billion in new cash, down slightly from the prior week's inflows of $1.9 billion.