VIENNA, Austria (CNN) -- A day before a key meeting on Iran's nuclear program, a "troubling" briefing in Vienna has revealed new information that Iran may be pursuing nuclear weapons, according to the U.S. ambassador to the International Atomic Energy Agency.

"The briefing highlighted many unanswered questions about (Iran's nuclear) program, and it also reported on new questions, including questions pointing directly to a military dimension, including the fabrication of nuclear weapons components and the design of missile re-entry vehicles," Greg Schulte said on Wednesday.

Schulte said a diplomatic settlement on thie issue was still possible if Tehran halted its nuclear activity, which Iran insists is for peaceful purposes only.

On Wednesday Iran's President Mahmoud Ahmadinejad angrily rejected international pressure on his country over its nuclear ambitions as U.S. President George W. Bush vowed to keep the Islamic republic from making an atomic bomb.

On Tuesday, the five permanent members of the U.N. Security Council -- Russia, China, Britain, France and the United States -- asked the IAEA to report Iran to the full Security Council.

And on Thursday, the IAEA board of governors will hold an emergency session at its Vienna headquarters to discuss a U.N. and EU-backed mandate calling on Iran to halt nuclear activity and return to the negotiating table.

The meeting could be the last step before Iran is referred to the Security Council.

"The reason why we're reporting this to the Security Council is to move diplomacy to a new phase so we can see if we can achieve a political settlement," Schulte said.

A flurry of diplomacy was taking place Wednesday, a last-ditch effort before the IAEA meeting to get Tehran to back off its stance.

In London, British Foreign Secretary Jack Straw on Wednesday met Iranian Foreign Minister Manouchehr Mottaki.

Before the meeting, Straw told BBC radio that he would urge Mottaki "to see this agreed position by the international community not as a threat but as ... a final opportunity to put itself back on track."

Later, British Prime Minister Tony Blair told the House of Commons that it was important to "send a signal of strength" to Iran.

"It is important that they understand ... that we are united in determining that they should not be able to carry on flouting their international obligations," he told MPs.

In his State of the Union speech on Tuesday, Bush said the world must act together to prevent Iran joining the list of nuclear-armed nations.

"The Iranian government is defying the world with its nuclear ambitions -- and the nations of the world must not permit the Iranian regime to gain nuclear weapons," Bush said in his Tuesday night speech. "America will continue to rally the world to confront these threats."

In Tehran, representatives from China and Russia carried the same message to Iranian officials in what European Union foreign policy chief Javier Solana called "one last effort to try to reach an agreement" before Thursday's IAEA meeting.

Representatives from the five permanent Security Council members-- the United States, Britain, France, Russia and China -- met in London Monday and agreed on the mandate, which Solana said also has the backing of the EU.

In addition to demanding Iran stop its nuclear activity, the mandate also calls on the U.N. Security Council to wait before taking any action against Iran until the IAEA board meets in March and hears a report from Director-General Mohammed ElBaradei on Iran's nuclear program.

But Iranian officials showed no sign of backing off their refusal to halt nuclear activity in the wake of international pressure.

"Our nation can't give in to the coercion of some bully countries who imagine they are the whole world and see themselves equal to the entire globe," Ahmadinejad said in a speech Wednesday.

Speaking in Bushehr, the site of Iran's nuclear power plant, the Iranian leader stood by the country's commitment to its nuclear program, which Tehran insists is for peaceful purposes.

"Nuclear energy is our right, and we will resist until this right is fully realized," Ahmadinejad said.

Iran's chief nuclear negotiator, Ali Larijani, said Wednesday that if the matter was referred to the U.N.'s Security Council, "it would be an improper and unsatisfactory measure which means a country would be punished for conducting research," according to Iran's state-run news agency.

On Tuesday Larijani warned that the recommendation to report Iran to the Security Council would be "the end of the road for diplomacy."

The U.S. believes Tehran has stepped up its preparations to enrich uranium ahead of a possible referral to the U.N. Security Council, a senior State Department official said Tuesday.

Since breaking IAEA seals at its nuclear facilities last month, Iranian nuclear activity has been "pretty consistent," with Tehran moving equipment to its nuclear facility at Natanz in preparation for enriching uranium -- activity the U.S. believes could be aimed at producing fissile material for a nuclear bomb, the official said.

Larijani said Wednesday his country would stop intrusive U.N. inspections of its nuclear facilities if it was taken before the Security Council.

However, he said his country remained committed to the Nuclear Nonproliferation Treaty despite calls from hard-line newspapers for Iran to withdraw from the agreement.

Many countries have been concerned that Iran has intended to use its nuclear program to develop weaponry.

Months of talks with European nations did not make headway in settling the issue, and discussions recently ended. Iran recently broke IAEA seals on its nuclear facilities, raising concerns in the West.

Straw said international pressure on Iran appeared to be having no direct effect on Iran's president, at least "in terms of rhetoric."

On Tuesday, oil ministers from the OPEC cartel warned that sending Iran's case to the Security Council could cause a spike in already sizzling oil prices. But Iran eased concerns it could use its status as the world's fourth biggest crude oil producer as a weapon in the dispute by curtailing its exports.

Also Tuesday, the IAEA said in a confidential report that Iran had already begun preparing for uranium enrichment and continued to hinder the U.N. watchdog's inquiries into its atomic activities. A senior U.S. State Department official gave a briefing on how Tehran had stepped up its preparations to enrich uranium.

Four years ago Bush used his State of the Union address to name Iran with North Korea and Iraq as nations that "constitute an axis of evil, arming to threaten the peace of the world".

With all sides engaged in high-stakes negotiations, he avoided such language on Tuesday, although he described Iran as "a nation now held hostage by a small clerical elite that is isolating and repressing its people."

Ahmadinejad fired back that Bush himself was a criminal.

"Those whose arms are stained up to the elbow with the blood of other nations are now accusing us of violating human rights and freedoms. God willing, we shall drag you to trial," he said.