U.S. Secretary of State Marco Rubio said there are "good signs" in ongoing negotiations with Iran but warns Washington has "other options" if diplomacy fails.

"There are some good signs,” Rubio told reporters but said: "I don't want to be overly optimistic, as well. So, let's see what happens over the next few days."

In talks with Iran, "I think we've made some progress,” Rubio said. "But obviously we're dealing with a system that itself is a little fractured.”

He said U.S. President Donald Trump’s preference was to "do a good deal.”

"It's always been his preference. If we can get a good deal done, that would be great. I'm not here to tell you that it's going to happen for sure, but I'm here to tell you that we're going to do everything we can to see we can get one,” Rubio said.