(JTA) – Nuclear talks between Iran and the world powers are likely to be extended further, with U.S. Secretary of State John Kerry saying, “Some of the tough issues remain unresolved.”

At a brief appearance before reporters on Thursday in Vienna, where the negotiations are taking place, Kerry did not specify any new deadline but said tough decisions must be taken very soon.

“We are not going to sit at the negotiating table forever. We also recognize that we shouldn’t get up and leave simply because the clock strikes midnight,” Kerry said in the Austrian capital. “Given that the work here is incredibly technical and that the stakes are very, very high, we will not rush and we will not be rushed.”

If the negotiations over curbing Iran’s nuclear program in exchange for relaxing sanctions drags on past Thursday, a congressional review of any agreement automatically will increase to up to 60 days rather than 30, according to a bill Congress passed this spring.

Earlier Thursday, the European Union’s high representative for foreign affairs, Frederica Mogherini, told CNN that the two sides are “very close, but if the important, historical, political decisions are not made in the next hours, we won’t (have) an agreement.”

Kerry said President Barack Obama is prepared to have the United States walk away if what Iran offers doesn’t pass muster.

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