US President Barack Obama has placed stricter sanctions on Iran's government, including its central bank.
In an executive order, Mr Obama said he was freezing all Iranian government assets held or traded in the US.
On Sunday, Mr Obama said the US and Israel were "in lockstep" in their policy towards Iran.
Concerns have grown in Israel and the West that Iran is developing nuclear weapons, although Tehran says its nuclear programme is entirely peaceful.
The new US sanctions include blocks on the Central Bank of Iran, imposed "in light of the deceptive practices" the bank to conceal transactions already banned by previous sanctions.
The curbs were also prompted by Iran's "deficient" efforts to combat money-laundering, the executive order said.
The US introduced new sanctions on Iran at the end of 2011 but stopped short of targeting the central bank.
Pre-emptive worries
Speaking on Sunday in an interview with NBC, the US president emphasised that Israel and the US were working in "unison" to counter Iran.
Washington had "a very good estimate" of when Iran could complete a nuclear weapon, Mr Obama said.
But knowledge of Tehran's internal decision-making was not as clear, he said.
"Do we know all of the dynamics inside of Iran? Absolutely not. Iran itself is a lot more divided now than it was. Knowing who is making decisions at any given time inside of Iran is tough.''
He stressed the US was attempting to resolve the showdown diplomatically but that the country had done extensive planning on all options.
Reports in the US media last week suggested Israel was planning to attack Iran in the spring of 2012, prompting an ambiguous response from US Defence Secretary Leon Panetta.
Source: BBC
My prediction threads:
Wii U will sell under 40m units (made on 14th September 2012)
PS Vita will sell under 20m units (made on 30th September 2012)
Wii U will sell under 7m in 2013 - I was right
