Federal Reserve Bank of Dallas President Robert Kaplan said he'll move closer to advocating for an interest-rate increase at the next policy meeting if economic data improves, as he suspects it will, with one caveat: Brexit.

"It'll be a factor," Kaplan said Friday about the U.K.'s approaching vote on whether to exit the European Union. If the result is uncertain heading into the June 23 referendum, that could roil currency and bond markets and "create some instability," he said in an interview on Bloomberg Television in London. Policy makers hold their next meeting on June 14-15.

"I'm going to have to make an assessment on June 15th what the likelihood is," said Kaplan, who doesn't vote this year on the policy-setting Federal Open Market Committee. "Right now it's unclear, and if it's still unclear on June 15, it is going to be a factor."