WASHINGTON (Reuters) - The U.S. economy has shown signs of improvement in recent weeks but the Federal Reserve expects it will take some time before it can assess the impact of Britain's vote to leave the European Union, Fed Vice Chair Stanley Fischer said on Friday.

A June 3 report showing a sharp slowdown in hiring during May and the risks around Britain's June 23 Brexit vote have raised concerns at the Fed over whether the U.S. economy was ready for more interest rate increases.

More recent economic data has eased some of those concerns, but Fischer gave no steer on when the Fed might raise rates.

"As we consider the effects of Brexit, we've got to put that effect on the U.S. together with what else is going on in the U.S. economy," he told CNBC in an interview. "Most of the incoming data look good now."

But the Fed will have a hard time assessing the impact of Britain's vote because the exit negotiations could take a long time and other countries might also seek to leave the EU.

"When it's something that is going to go on and unwind over the course of time, it's much harder," Fischer said in an interview with U.S. network CNBC.

Fischer said the Fed would like to know "how quickly the British economy reaches its new configuration with new trade... And then there are the concerns about implications of the British example for other countries."

(Reporting by Jason Lange and Howard Schneider; Editing by Chizu Nomiyama and Frances Kerry)