US Secretary of State Anthony Blinken and the nominee for his deputy, Wendy Sherman, stressed on Wednesday the need for Iran's compliance before returning to the 2015 nuclear deal.
“We have to ensure that Iran does not obtain a nuclear weapon; that there be compliance for compliance, as the president said,” Ms Sherman told Congress.
Mr Blinken, speaking from the State Department, outlined eight objectives for the Biden administration's foreign policy.
They include a less militaristic approach, fighting the pandemic, advocating for democracy, addressing climate change and countering China.
On the Middle East, Mr Blinken repeated the administration’s willingness to return to the 2015 nuclear deal between Iran and world powers, but when Tehran returned to compliance.
He said the US was committed to diplomacy but was not opposed to using force when necessary.
“Diplomacy, not military action, will always come first,” he said.
But the Biden administration “will never hesitate to use force when American lives and vital interests are at stake".
"That's why President Biden authorised an air strike last week against Iranian-backed militia groups targeting US forces in Iraq," he said, referring to the strike carried out on February 25.
“But in that case and in future cases when we must take military action, we will do so only when the objectives and mission are clear and achievable, consistent with our values and laws, and with the informed consent of the American people.
"And we’ll do it together with American diplomacy.”
Mr Blinken called China the "biggest geopolitical test of the 21st century" because of its ability to challenge the international system.
“China is the only country with the economic, diplomatic, military and technological power to seriously challenge the stable and open international system,” he said.
Most of the questions Ms Sherman fielded from senators in her confirmation hearing dealt with Iran, and the nuclear deal in particular.
“I remain clear-eyed about the threat that Iran poses to our interests and those of our allies,” Ms Sherman told the Senate foreign relations committee.
“I would note that 2021 is not 2015 when the deal was agreed, nor 2016 when it was implemented.
"The facts on the ground have changed, [the region has] changed and the way forward must similarly change.”
Ms Sherman was the lead negotiator for the Iran nuclear deal when she was undersecretary of state for political affairs under the Obama administration.
The Trump administration withdrew from the accord in 2018, placing stringent sanctions on Iran.
Iran has since increased its breaches of the accord and rebuffed a European-brokered attempt for direct talks with the US on Sunday.
“Iran is a long way from compliance, as we all know,” Ms Sherman said of possible US sanctions relief.
“The decisions that need to be taken will be along the lines of those laid out by the president of the United States and the secretary of state, and indeed have to be decided on the merits of where we are today, not nostalgia for where we might have been."