By Paul Reynolds
World affairs correspondent, BBC News website
Yukiya Amano urged Iran to co-operate in clarifying outstanding issues
The latest report on Iran by the UN's nuclear watchdog, International Atomic Energy Agency (IAEA), reflects a tougher approach by the agency under its new director-general.
But while the language is stronger, it is less clear that the evidence is. There are still more questions than answers.
The effect, though, is that the headlines taken from this report are more dramatic and the arguments for sanctions are more pronounced.
What has happened with this report is that the new IAEA chief, Yukiya Amano, a Japanese lawyer and diplomat, is more open in saying that Iran's activities do raise concerns, not just about its past programmes but about its present.
The key new word here is "current".
"The information available to the agency... is extensive... and broadly consistent and credible in terms of the technical detail... [and] raises concerns about the possible existence in Iran of past or current undisclosed activities related to the development of a nuclear payload for a missile," Mr Amano says.
"Iran needs to co-operate in clarifying outstanding issues which give rise to concerns about possible military dimensions," he adds.
You can see the difference by looking at the more cautious approach under the previous director-general, Mohamed ElBaradei.
Mr ElBaradei said there "no credible evidence" about a weapons attempt
In his last report in November 2009, this was the phrasing: "There remain a number of outstanding issues which give rise to concerns, and which need to be clarified to exclude the existence of possible military dimensions to Iran's nuclear programme."
Where Mr ElBaradei avoids the word "current" and is reluctant to link his "concerns" to "possible military dimensions", Mr Amano does just that.
Where his predecessor delicately sought Iranian answers in order to "exclude" the existence of "possible military dimensions", Mr Amano comes out and says there is "credible" evidence behind those concerns.
The difference might not appear large, but in the language of nuclear diplomacy it is significant.
So what are these concerns based on?
Iran says it is increasing uranium enrichment from 3.5% needed for commercial nuclear reactors
Iran says it has started enriching to 20%, needed for a research reactor near Tehran
Weapons-grade uranium is at least 90% enriched
Experts say achieving 20% is a key step towards weapons grade
First, it is worth noting that they are not wholly about uranium enrichment. That gets most of the headlines.
The IAEA is monitoring Iranian enrichment and continues to confirm that declared material has not been diverted (to nuclear weapons use), though this time the statement is not unqualified as it usually is.
A caveat has been added saying that Iran has not given enough information to allow the IAEA to "confirm that all nuclear material in Iran is in peaceful activities".
The concerns are also to do with other activities, about which Iran remains largely unresponsive.
The latest report lists them - notably whether Iran developed a "spherical implosion system" for a nuclear warhead; whether designs for a missile payload were for a nuclear device; plus "activities involving high-precision detonators; studies on the initiation of high explosives and missile re-entry body engineering; a project for the conversion of UO2 [uranium dioxide] to UF4 [uranium tetrafluoride], known as the 'green salt project'; and various procurement activities".
Some of the "broadly consistent and credible" evidence on which this is based came from a laptop produced by the US and said to be from an Iranian source.
Iran's government insists its nuclear programme is entirely peaceful
Iran has refused to give detailed replies to these allegations because it says the information was forged.
The IAEA has known about these allegations for some time.
What it is now more open about saying is that all these alleged activities (plus others like the development of a heavy-water reactor to which the IAEA has been denied access) form the basis for the "concerns about possible military dimensions."
In plain language, it means that there are fears that Iran has studied elements of bomb-making in the past and - the new point - it cannot be ruled out that they are still doing so.
This does not mean that they are. The Iranians deny it and their Supreme Leader, Ayatollah Ali Khamenei, has just repeated that Iran does not intend to make a nuclear bomb.
However, the IAEA report will probably strengthen the hand of those wanting to increase sanctions on Iran, discussions about which are currently going on in the UN Security Council.