Leon Panetta, the United States defence secretary, has told US legislators that while Iran is enriching uranium for its nuclear programme, there are currently no indications that Tehran has decided to develop atomic weapons.
Panetta and other top US intelligence officials offered insights and observations into Iran's disputed nuclear programme during separate congressional hearings in Washington on Thursday.
Their testimony came as Iran boasted of major advances in producing nuclear fuel and threatened an oil embargo in retaliation for a raft of economic and diplomatic sanctions being imposed by the United States and the European Union.
Israel, meanwhile, has accused Iran of being responsible for recent attacks on Israeli diplomats in Thailand, Georgia and India, and has threatened military strikes against Iranian nuclear facilities.
"We will not allow Iran to develop a nuclear weapon," Panetta told the House Appropriations Committee's defense subcommittee on Thursday.
"We will not allow Iran to close the Strait of Hormuz. And in addition to that, obviously, we have expressed serious concerns to Iran about the spread of violence and the fact that they continue to support terrorism and they continue to try to undermine other countries."
The Pentagon chief reiterated, as US President Barack Obama often has in recent months, that the US keeps "all options on the table".
Panetta, the former director of the Central Intelligence Agency, said that US intelligence showed that Iran was continuing its uranium enrichment programme.
"But the intelligence does not show that they've made the decision to proceed with developing a nuclear weapon. That is the red line that would concern us and that would ensure that the international community, hopefully together, would respond," he said.
Speaking in front of the US Senate's Armed Services Committee, James Clapper, the director of national intelligence, said that the decision to pursue nuclear weapons would be made by Ayatollah Ali Khamenei, Iran's supreme leader.
"[Khamenei] would base that on a cost-benefit analysis in terms of, I don't think he'd want a nuclear weapon at any price," Clapper said. "So that I think plays to the value of sanctions, particularly the recent ratcheting up of more sanctions and anticipation that that will induce a change in their policy and behaviour."
Clapper said that it was "technically feasible" that Tehran could produce a nuclear weapon in one or two years, if its leaders decide to build one, but that it was "not likely", in practical terms.
The United States imposed new sanctions on Iran's central bank, the latest round of penalties that have won widespread bipartisan support in the US Congress.
The Treasury Department announced on Thursday that it was imposing sanctions on Iran's ministry of intelligence and security, asserting that it supported global terrorism and had committed human rights abuses against Iranians and participated in ongoing repression in Syria.
The new sanctions freeze any assets the ministry may have in US jurisdiction, bars US citizens from doing business with it and ban employees of the ministry from travelling to the United States.
It is unclear what effect the ban will have, as the ministry is not known to have holdings in the United States.
Panetta and legislators have insisted that the sanctions as a whole are taking an economic toll on Iran.
Binyamin Netanyahu, the Israeli prime minister, meanwhile, has said that the sanctions have not been effective, though some of his cabinet ministers have dissented from this opinion.
Despite the tough talk from Netanyahu on Israel, Clapper and Defence Intelligence Agency chief Lieutenant-General Ronald Burgess said on Thursday that they did not believe that Israel had made the decision to strike at Iran.
If Iran is attacked, however, Burgess said that it could "close the Strait of Hormuz, at least temporarily, and may launch missiles against United States forces and our allies in the region".
"Iran could also attempt to employ terrorists' surrogates worldwide. However, the agency assesses Iran is unlikely to initiate or intentionally provoke a conflict," he said.