The US Federal Reserve board has decided not to increase interest rates because of developments that could stall global growth. But Fed chair Janet Yellen has left the door open to raising rates again before the end of the year. 

U.S. central bank chief, Janet Yellen, assured global investors, Wednesday, that she's leaving American interest rates where they are - for now.

"Proceeding cautiously in raising our interest rate target, will allow us to verify that economic growth returns to moderate pace, that labor market will strengthen further," Janet Yellen said.

Part of the problem is weakness in the U.S. economy. Two weeks ago, analysts saw signs of softening in the labor market here. May brought the fewest number of new jobs in more than five years.

"Although this recent labor market report was, on balance, concerning..." Janet Yellen said.

Yellen told an audience in Philadelphia a few days later, the overall economic prognosis was positive, but global developments are also clouding the outlook for U.S. growth.

Oil prices have been falling since the beginning of 2016-that's hurt the U.S. energy sector. And then there's the looming Brexit-Britain's possible exit from the EU after next week's referendum-a risk already roiling global stock markets. Yellen says that weighed on the minds of central bank governors.

"It's a decision that could have consequences for economic and financial conditions in global financial markets. If it does so," Janet Yellen said.

The FED also signaled there was room for two more rate increases by the end of 2016-if the current economic outlook improves. Economists say raising rates would have the added benefit of discouraging excessive risk-taking in the stock market.