WASHINGTON — Secretary of State John Kerry took a brief break from his rigorous travel schedule to the Middle East on Tuesday to press Congress to hold off on additional sanctions against Iran, describing such legislation as “gratuitous” and potentially damaging not only to any future deal with the Islamic Republic, but also to America’s relations with fellow states in the P5+1 group.

“Let me be very clear: This is a very delicate diplomatic moment and we have a chance to address peacefully one of the most pressing national security concerns that the world faces today,” Kerry told the House Foreign Affairs Committee. “We’re at a crossroads. We’re at one of those really hinge points in history. One path could lead to an enduring resolution in the international community’s concerns about Iran’s nuclear program. The other path could lead to continued hostility and potentially to conflict.”

Kerry’s comments shed light on Washington’s flexibility on the terms of a final-status agreement. While he said that the interim agreement reached last month in Geneva rendered the Arak heavy water facility “frozen stone-cold,” he did not rule out the possibility of future negotiations over the fate of the plant, which could be used to produce plutonium for a nuclear bomb.

The secretary of state also avoided any commitment to the effect that the final agreement would prohibit Iran entirely from enriching its own uranium.

Kerry assured Congress that during the interim period, while the P5+1 member states are negotiating a final agreement, “Iran’s nuclear programs will not move forward.” Instead, he promised, “this agreement halts the progress of Iran’s nuclear program and rolls its back in certain places.”

In response to a question by Rep. Eliot Engel (D-NY), Kerry said that the United Arab Emirates and Saudi Arabia had welcomed the deal because it provided new-found security. He acknowledged, however, that Israel did not find the deal reassuring.

Anticipating being pressed by members of Congress on the repeal of sanctions placed on Iran by Congressional mandate, Kerry told the committee that the estimated $7 billion in sanctions relief that would result from Iran’s compliance with the interim agreement “pales in comparison with the amount of pressure we’re leaving in place.”

Describing additional sanctions as “gratuitous,” Kerry emphasized that he would not rule out such legislation in the future.

The interim deal with Iran prohibits the Obama administration from introducing new sanctions for six months. Kerry and other US officials have warned of dire consequences if Washington breaks its word. And Iran’s foreign minister, Mohammad Javad Zarif, has said any new package of commercial restrictions would kill the deal.

“If Congress adopts sanctions, it shows lack of seriousness and lack of a desire to achieve a resolution on the part of the United States,” Zarif told Time magazine.

“I’m just saying ‘not right now.’ This is a very delicate diplomatic moment,” Kerry explained on Tuesday, arguing that were Congress to finalize additional sanctions, it could result in the Iranians pulling out of talks, or disunity among fellow members of the P5+1 negotiating team.

“I don’t want to give the Iranians a public excuse to flout the agreement,” Kerry said. “It could lead our international partners to think that we’re not an honest broker, and that we didn’t mean it when we said that sanctions were not an end in and of themselves but a tool to pressure the Iranians into a diplomatic solution. Well, we’re in that. And six months will fly by so fast, my friends, that before you know it, we’re either going to know which end of this we’re at or not.”

Members of both parties challenged Kerry. Engel, the top Democrat on the panel, specifically asked Kerry why the administration was so strongly opposing sanctions that wouldn’t be imposed unless Iran breaks the agreement. And Democratic Rep. Brad Sherman expressed misgivings about trusting the Obama administration, which he accused of hampering all sanctions efforts against Iran thus far.

As Kerry spoke, reports circulated that the secretary of state will address Iran sanctions before the full Senate on Thursday in an intensified effort to keep the upper house from voting on a sanctions bill before it goes on its winter recess.

Members of Congress generally believe that crippling petroleum, banking and trade sanctions levied on Iran in recent years were responsible for bringing its more moderate president, Hassan Rouhani, to power and his representatives to the negotiating table. Many argue more pressure, not less, could break Iran’s will and secure better terms in a final agreement.

At several points, Kerry and lawmakers talked over each other as they argued about whether the deal recognized Iran’s “right” to enrich uranium — which the administration rejects — and about the details of international inspections on Iranian sites and its non-nuclear weapons programs.

Rep. Ileana Ros-Lehtinen, R-Fla., was perhaps strongest in her criticism of the administration, flatly denouncing the agreement in Geneva as a “bad deal.”

“We may have bargained away our fundamental position,” said Rep. Ed Royce, R-Calif., the committee chairman. “Iran should not be enriching and reprocessing,” he said, criticizing what he termed the administration’s “false confidence that we can effectively check Iran’s misuse of these key nuclear bomb-making technologies.”

Iran insists its program is solely for peaceful nuclear energy and medical research.