Obama told NBC that he would work to prevent Iran obtaining a nuclear weapon
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” of 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.
A raft of new sanctions were passed by Congress in December 2011 as part of a wide-ranging defence bill, despite warnings from the White House that including sanctions against the Iranian central bank would interfere with the foreign relations of US allies.
Knowing who is making decisions at any given time inside of Iran is tough”
While Mr Obama signed the bill he said he reserved the right to treat the provisions as non-binding, angering some hawks on Capitol Hill who questioned his commitment to increasing pressure on Iran, says BBC Persian’s Mohammad Manzarpour, in Washington.
By issuing this executive order, President Obama seems to be trying to discredit those who claim he is not serious about sanctions, while still exercising some leeway when it comes to the dealings of his key allies with Iran, our correspondent says.
The executive order gives American institutions the powers to freeze assets related to the Central Bank of Iran, instead of just turning them back.
In a statement, the US Treasury department said the order was part of “the administration’s resolve to hold the Iranian regime accountable for its failure to meet its international obligations”.
Iran “will face ever-increasing economic and diplomatic pressure” until it answers the international community’s “well-founded and well-documented concerns” about its nuclear programme, the Treasury said.
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?” said Mr Obama. “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.
Asked if he believed the Jewish state could launch a pre-emptive strike against Iran, Mr Obama said: “I don’t think Israel has made a decision on what they need to do.”
He declined to answer directly a question whether Washington would be consulted first, saying only that the US and Israel “have closer military and intelligence consultation… than we’ve ever had”.
However, correspondents say that behind the scenes Washington is deeply alarmed by reports that Israel may strike Iran as early as April.
US media last week suggested Israel was planning to attack Iran in the spring of 2012, with US Defence Secretary Leon Panetta reportedly saying there was a strong likelihood of such an offensive.