Huh?

So now the US intelligence agencies think Iran shut down a nuclear weapons program four years ago. Well, sounds like that's that, doesn't it? Problem solved...
Not so fast -- here's the National Security Advisor's reaction:

Mr. Hadley said the latest intelligence estimate was ' positive news' and called for even tougher sanctions on Tehran. 'The international community has to turn up the pressure on Iran — with diplomatic isolation, United Nations sanctions, and with other financial pressure — and Iran has to decide it wants to negotiate a solution,' he said.

Why, exactly, would "even tougher sanctions" be warranted? What on-going problem are they supposed to be negotiating" a solution" to?