WASHINGTON, May 23 (Xinhua) -- U.S. Secretary of State Antony Blinken said on Sunday that it remains unclear if Tehran is willing to take steps to return to compliance with the Iran nuclear deal.

"The outstanding question, the question that we don't have an answer to yet, is whether Iran, at the end of the day, is willing to do what is necessary to come back into compliance with the agreement," Blinken said in an interview with CNN.

He raised the same question during an interview with ABC on Sunday morning. The top U.S. diplomat said that the indirect talks between Washington and Tehran in Vienna had clarified what each side needs to do to come back into compliance with the Iran nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA).

"And what we haven't yet seen is whether Iran is ready and willing to make a decision to do what it has to do. That's the test and we don't yet have an answer," he added.

The United States and the remaining parties to the JCPOA -- Iran, Britain, China, France, Germany, and Russia -- will reconvene next week for the fifth-round talks in Vienna aimed at reviving the nuclear deal.

Iranian President Hassan Rouhani said earlier in the day that Iran would continue nuclear talks until a final agreement is reached, the official IRNA news agency reported.

Rouhani said on Thursday that the "main agreement" to revive the nuclear deal had already been reached in the talks, and Iran's counterparts have agreed on the need to lift "all main sanctions."

The U.S. government under former President Donald Trump withdrew from the JCPOA in May 2018 and unilaterally re-imposed sanctions on Iran. In response, Iran gradually stopped implementing parts of its JCPOA commitments from May 2019.