The U.N. nuclear watchdog ends its latest mission to Iran after talks on Tehran's suspected secret atomic weapons research failed -- a setback analysts say will likely increase the risk of confrontation with the West.

In a defiant response, Iran's Supreme Leader Ayatollah Ali Khamenei said Iran's nuclear policies would not change.

(SOUNDBITE)(Farsi) IRAN'S SUPREME LEADER AYATOLLAH ALI KHAMENEI, SAYING:

"When a nation makes the decision to stand, sanctions and political pressure will have no impact."

He also said that Iran is seeking nuclear power for peaceful purposes only.

(SOUNDBITE)(Farsi) IRAN'S SUPREME LEADER AYATOLLAH ALI KHAMENEI, SAYING:

"We want to say that we are not in pursuit of nuclear weapons and we don't see power in (the possession of) nuclear weapons and we can break the dependence on nuclear weapons, and God willing the nation will do this."

The collapse of the nuclear talks comes as Iran seems increasingly isolated. Some experts see the Islamic republic's mounting defiance in response to sanctions against its oil industry and financial institutions as evidence that it is in no mood to compromise with the West.

The failure of the two-day visit by the International Atomic Energy Agency could now hamper any resumption of wider nuclear negotiations between Iran and six world powers.

In the view of some analysts, the Iranians may be trying to keep their opponents guessing as to their capabilities, a diplomatic strategy that has served them well in the past.

The United States and Israel have not ruled out using force against Iran if they conclude that diplomacy and sanctions will not stop it from developing a nuclear bomb.

Deborah Lutterbeck, Reuters.