The governments fear that a concerted effort to persuade Trump to continue to certify the deal may have failed and hence are now looking for other ways, The Guardian reports.
The U.S. State Department is due to certify Congress whether Iran has been complying with the terms of the deal, formally known as the Joint Comprehensive Plan of Action, or JCPOA.
European lobbying efforts are now focused on Congress, which will have two months to decide - in the absence of Trump's endorsement of the 2015 deal - whether to reimpose nuclear-related sanctions.
Trump had said he has made up his mind already, but did not tell the European leaders his decision, including British Prime Minister Theresa May, who reportedly asked him at a bilateral meeting at the UN last month.
However, the U.S. Defence Secretary James Mattis on Tuesday openly contradicted Trump's position on the Iran nuclear deal, while testifying in front of Congress, by backing the nuclear deal with Iran and saying it is in the interests of national security to maintain it.
During a Senate Armed Services Committee hearing, Mattis was asked whether he believed it was currently in the US national security interest to remain in the agreement.
After a significant pause, he replied, "Yes, senator, I do."
Under the relevant legislation, the administration has to certify whether Iran is in material breach of the agreement, or if the deal is not serving the national interest.
Under the U.S. law, Trump has until October 15 to certify that Iran is complying with the nuclear deal. If he declines to certify Iran, then Congress will have the option to re-impose sanctions on Iran, which would effectively end the deal. (ANI)