Kerry: ‘Substantial progress’ with Iran but no deal yet
According to the Associated Press, Kerry said the U.S. isn’t rushing to finish the deal just for the sake of beating the self-imposed March 31 deadline. 
"We don't want just any deal," he said. "If we had, we could have announced something a long time ago."
Kerry is scheduled to meet with British, French and German officials in London on Saturday. Negotiations with Iran continue next week in Lausanne, Switzerland.
Kerry said the United States’ negotiating partners are "united in our goal, our approach, our resolve and our determination."
Speaking from Tehran, Iranian President Hassan Rouhani said “there is nothing that can’t be resolved” in the negotiations.
"Achieving a deal is possible," he said.
- Updated at 8:51 a.m.