United States Defense Secretary Jim Mattis said Tuesday that remaining in the Iran nuclear accord is in Washingtons national security interests contradicting with President Donald Trump, who has called the deal agreed between Iran and six world powers in 2015 an “embarrassment.” During testimony before the Senate Armed Services Committee on Tuesday, the countrys top defense official was asked by a senator if remaining in the deal is in the national security interests of the US. After a lengthy pause, he answered: "Yes senator, I do." "If we can confirm that Iran is living by the agreement, if we can determine that this is in our best interest, then surely we should stay with it," he added. "I believe at this point in time, absent indication to the contrary, it is something that the president should consider staying with," he said, according to AFP. Trump must notify Congress every 90 days whether Iran is abiding by the accord and whether the lifting of sanctions against Tehran is in the US national interest. He has so far certified that Iran is in compliance with the agreement but has indicated the next deadline on October 15 will be crucial. Iran and the other signatories -- China, Russia, France, Britain and Germany -- defend the deal, which was signed in 2015, as a guarantee of the peaceful, non-military purposes of Tehrans nuclear program. Mattis also warned earlier in his remarks that a US withdrawal from Afghanistan would be "to our ultimate peril," as he briefed Congress on plans to increase US troop levels. "Based on intelligence community analysis and my own evaluation, I am convinced we would absent ourselves from this region at our peril," he said. Mattis said that more than 3,000 additional US troops are being sent to Afghanistan to reinforce the 11,000 US troops already stationed in the country. He also said that the United States will soon decide whether to keep open a Taliban office in Qatar as America steps up its Afghan war effort. Mattis said he and Secretary of State Rex Tillerson had been "in contact on this issue three times in the past 10 days." "He is looking to make certain we have the right [Taliban representatives], so its just not an office in existence," he added. In this context, the US has ordered the expulsion of 15 Cuban diplomats on Tuesday, accusing Havana of failing to protect their American counterparts from harm in a series of attacks on their health. Tillerson said, however, that Washington would maintain diplomatic relations even though the size of the US mission in Havana would be reduced to a minimum. "Until the government of Cuba can ensure the safety of our diplomats in Cuba, our embassy will be reduced to emergency personnel to minimize the number of diplomats at risk of exposure to harm," he said. "This order will ensure equity in our respective diplomatic operations," he said. The attacks, which US officials initially suggested could have been carried out with some sort of covert acoustic device, have affected at least 22 US embassy staff in Havana over the past few months. Those affected have exhibited physical symptoms including ear complaints, hearing loss, dizziness, headache, fatigue, cognitive issues, and difficulty sleeping.