The announcement of Kerry's trip came a day after his counterpart from Britain, one of six powers negotiating with Iran ahead of Monday's cut-off point, expressed pessimism that the mammoth accord could be done in time.
"I am not optimistic that we can get everything done by Monday," British Foreign Secretary Philip Hammond said in Latvia.
The best to be hoped for, he indicated, was another extension, but only if there is "significant movement".
Iran and the five permanent members of the UN Security Council plus Germany have been negotiating since February to turn an interim accord with Iran reached a year ago into a lasting agreement before November 24.
Such a deal, after 12 years of rising tensions, is aimed at easing fears that Tehran will develop nuclear weapons under the guise of its civilian activities -- an ambition the Islamic republic has always denied.