WASHINGTON  - Washington on Thursday blacklisted a dozen overseas companies and individuals for evading sanctions on Iran in a clear warning to Tehran to comply with a nuclear deal, and persuading US lawmakers to hold off on new punitive measures. Only hours after the surprise announcement, two top senators bowed to White House pleas not to introduce new sanctions, acknowledging it could “rupture” unity among global powers seeking to rein in Iran’s suspect nuclear enrichment program.

“Let me be clear. I support strong sanctions, and authored many of the US sanctions currently in place,” said Senate banking committee chairman Tim Johnson, who has been in the spotlight over whether he would introduce a new sanctions regime this year, as several senators have sought. “But I agree that the administration’s request for a diplomatic pause is reasonable,” Johnson told a hearing. Under Thursday’s designations, US citizens or companies are barred from engaging in transactions with any of the targeted firms and individuals whose assets will be also be frozen in the United States. “Today’s actions should be a stark reminder to businesses, banks and brokers everywhere that we will continue relentlessly to enforce our sanctions, even as we explore the possibility of a long-term, comprehensive resolution of our concerns with Iran’s nuclear program,” said David Cohen, Treasury under secretary for terrorism and financial intelligence.

Those listed include the Singapore-based Mid Oil Asia and Singa Tankers, both companies accused of helping Iran transfer badly-needed funds to a foreign bank on behalf of the National Iranian Tanker Company. Ukrainian national Vitaly Sokolenko and his Odessa-based firm Ferland Company Limited were also cited for helping to broker the sales of Iranian oil and transfer the crude ship-to-ship. US Secretary of State John Kerry this week returned twice to Capitol Hill seeking to dissuade lawmakers from drawing up new legislation and urging that diplomacy be given time to work.

Under an interim deal reached in Geneva last month, Iran agreed to freeze parts of its suspect nuclear program in return for some $7 billion in sanctions relief as it negotiates a final, comprehensive accord to dismantle its nuclear weapons capability. The United States also agreed to refrain from slapping new sanctions on Iran, but senior administration officials argued that Thursday’s measures were taken as part of the existing sanctions regime which had forced Tehran to the negotiating table.

“Sanctions pressure will be essential as we seek to negotiate a comprehensive long-term resolution,” a senior administration official told reporters on a conference call. “The message to the Iranian government remains clear, the only escape from increasing sanctions pressure, the only path out of deepening economic distress is to negotiate and make the necessary concessions to address the international community’s concerns with their nuclear program.”

Despite Johnson’s move Thursday he made clear that he was already crafting new sanctions behind closed doors which could be acted on quickly if Iran fails to comply with the terms of the November 24 deal. Johnson’s fellow Senate Democrat Robert Menendez and Republican Mark Kirk have also been drafting a bill that they want to see passed sooner rather than later imposing tough new economic sanctions if Iran reneges on the six-month accord.

The senior administration official had dismissed the notion, however, that Thursday’s designations were aimed at sending a message to Congress to lay off new sanctions, saying they had only been announced once State Department and Treasury had all the evidence in place. The US State Department also named five Iranian entities and several people that it alleges provide goods and services that contribute, or risked contributing, to Iran’s nuclear program or its development of ballistic missiles.

The US official also warned that the limited sanctions relief promised under the Geneva deal, did not mean that Iran was now open for international business again.

“There’s no reason to think that there’s great business opportunity in Iran today. The majority of their banks remain isolated from the international financial system,” the senior official administration official stressed. And he warned that the energy sector - most notably Iran’s vast oil reserves — remained subject to stringent sanctions