A high-level team from the United Nations' nuclear watchdog is in Iran for talks that could help determine whether a diplomatic solution can be found to the crisis over Tehran's nuclear ambitions.
The International Atomic Energy Agency (IAEA) wants Iran to address suspicions that its nuclear programme has a military intent. That means providing access to Iranian scientists, a suspect military complex and sensitive documents.
The leader of the five-man IAEA delegation, Herman Nackaerts, said he hoped for "concrete results", but cautioned progress "may take a while". His team's two-day mission to Iran, the second in as many months, wraps up today.
A goodwill gesture from Tehran could stave off another round of sanctions and defuse the threat of Israeli military action against Iran's nuclear facilities.
Tehran, which insists its nuclear activities are solely peaceful, has sent mixed signals to the West in recent days. It has declared "major" advances in its uranium enrichment programme, launched new war games and ordered the halt of oil exports to Britain and France in retaliation for a phased European ban on Iranian oil imports.
Iran has also belatedly accepted a four-month-old invitation to resume nuclear talks with six world powers - the US, China, Russia, Britain, France and Germany - and promised to bring "new initiatives" to the table.
How far Tehran co-operates with the IAEA team will be seen as a key test of its intentions as it enters the new negotiations. Meanwhile, fearing a new war in the Middle East, the US and Britain at the weekend urged Israel to exercise restraint and allow time for diplomacy and sanctions to work.
Yesterday, Iran announced two of its warships had docked at the Syrian port of Tartus, in a defiant show of support for the Syrian president, Bashar Al Assad.
The Iranian regime has an interest in showing goodwill in the battle for public opinion at home and abroad. With parliamentary elections in less than two weeks, Iran's rulers want to assure jittery voters that they are not responsible for unprecedented western sanctions targeting the country's oil exports, the heart of Iran's economy. The cost of living for Iranians has soared in recent weeks.
Mr Nackaerts is seeking explanations for evidence, described as "credible" in a report by the IAEA in November, pointing to past experimentation on nuclear weapons design. Iran had refused to discuss the allegations for more than three years, saying they are based on "fabricated documents" provided by hostile intelligence agencies.
But Iran signalled last month it was prepared to address the issue, insisting it had nothing to hide.
Tehran's boast last week that it has introduced a new generation of centrifuges to its uranium-enrichment efforts was dismissed by western officials as "hyped" and a show of bravado.
Iran's intention, many analysts believe, was to strengthen its negotiating hand in any new nuclear negotiations by establishing facts on the ground that could be rolled back as concessions if needed.
Tehran on Sunday said it wants a "win-win" solution from the talks and loftily declared it understood the West's need to "save face".
But mutual mistrust runs deep, dimming any early prospect of a diplomatic resolution. Many western officials suspect Iran has agreed to the new talks with the major powers only to stall for time as it presses ahead with its nuclear programme.
Tehran, in turn, fears the US's ultimate aim is to overthrow Iran's hardline clerical system of rule.
Iran's ban on oil sales to Britain and France was a symbolic gesture because neither country relies on Tehran for energy needs. But it rattled oil markets concerned the ban would be extended to countries like Greece, Italy and Spain, which receive Iranian oil on discount.
The head of Iran's Revolutionary Guards scoffed yesterday that the West had scored a goal by sabre-rattling in the Gulf.
"The crisis they have provoked in the region has led to a hike in oil prices, and they are feeling the impact," General Mohammad Ali Jafari told state television.
Tehran insists it can easily find Asian buyers to compensate for any loss to the EU, but the Financial Times reported yesterday Iran was finding this difficult because it was not offering any discount.