TEHRAN: The head of the UN nuclear agency arrived Monday in Tehran on a key mission that could lead to the resumption of probes by the watchdog on whether Iran has secretly worked on an atomic weapon.

It would also strength the Islamic Republic's negotiating hand in crucial nuclear talks with six world powers later this week in Baghdad.

International Atomic Energy Agency chief Yukiya Amano and his two aides were quickly whisked away after landing at the Tehran airport before dawn Monday. They are to meet Iran's top nuclear negotiator, Saeed Jalili, as well as Iran's foreign minister and other officials later in the day.

The visit — Amano's first since becoming the IAEA chief in 2009 — is focused on getting Iran to agree to terms that will allow IAEA probes of suspect Iranian sites, including the Parchin military complex where the agency had reported suspicious activities in the past.

Tehran denies having worked on atomic weapons, saying Parchin is only a conventional weapons site.

Inspecting Parchin, southeast of the capital Tehran, was a key request made by senior IAEA teams that visited Tehran in January and February. Iran rebuffed those demands at the time.

But with both Iran and the IAEA reporting progress in a previous round of talks last week, anticipation ahead of the visit was high. While expressing some optimism, Amano said he could not predict whether he would clinch a deal that would allow his agency to renew its long-stalled probe.

''Nothing is certain in life, in diplomacy,'' he told reporters before departing from the Vienna airport. ''But there has been good progress. ' 'I really think this is the right time to reach agreement,'' he added.

Amano's one-day trip is significant both for what it can achieve in terms of probing Iran's secretive nuclear program and as a mood-setter for talks Wednesday in Baghdad between Iran and the United States, Russia, China, Britain, France and Germany.

The six world powers are at the forefront of trying to persuade Tehran to curb its nuclear program and ease concerns it wants to use it to make nuclear weapons. For its part, Iran will seek to stay looming US and European Union sanctions on its oil exports at the Baghdad talks.

The six will attempt to get Iran to commit to stop enriching uranium to a level that can be turned quickly into the fissile core of nuclear warheads, while ignoring — for now — its program of lower enrichment, which would take longer to turn toward weapons-making. Iran insists it is enriching uranium only to produce nuclear fuel and for cancer treatment. It denies that it worked secretly on developing components of a nuclear arms program, despite what the IAEA describes as credible intelligence and other evidence that it hid work ''specific to nuclear weapons.''

Parchin is especially significant since the IAEA believes Iran in 2003 ran explosive tests needed to set off a nuclear charge. The suspected blasts took place inside a pressure chamber. Iran has never said whether the chamber existed.

As Amano arrived, Iranian lawmaker Heshmatollah Falahtpisheh told The Associated Press that Tehran will likely accept more inspections of Parchin, ''if it feels there is good will within the (IAEA) agency.''

But Falahtpisheh, a member of the influential parliamentary committee of national security and foreign policy, warned that this new openness will likely come with expectations that the West would in return ease international sanctions on Iran.

''In opening up to more inspections, Iran aims at lowering the crisis over its nuclear case,'' said Falahtpisheh. ''But if the sanctions continue, Iran would stop this.''

A political analyst in Tehran, Hamid Reza Shokouhi, said Iran is carefully watching to see if the West shows more ''flexibility and pays attention to Iranian demands'' during Amano's trip.

''Then Iran will show flexibility, too,'' said Shokouhi.