BRUSSELS -- The U.S. is not ready to collaborate militarily with Russia, Defense Secretary Jim Mattis said Thursday, appearing to close the door for now on any effort to work more closely with Moscow in the fight against the Islamic State of Iraq and Syria, or ISIS, in Syria.

His blunt rejection came after Russian President Vladimir Putin called for increased intelligence cooperation with the U.S. and NATO, and it makes such coordination less likely at least in the near future. Mattis followed his dismissal with a sharp assessment of Russia’s alleged election meddling, saying there is “very little doubt that they have either interfered or they have attempted to interfere in a number of elections in the democracies.”

His comments raised questions about the Trump administration’s policies on Russia. As a candidate, President Trump repeatedly praised Putin, saying he wanted a new era of cooperation with Moscow.

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Speaking at a meeting of NATO defense ministers, Mattis said the U.S. will continue to engage politically with Putin’s government to try to find common ground.

Political leaders, Mattis said, will seek “a way forward where Russia, living up to its commitments, will return to a partnership of sorts here with NATO. But Russia is going to have to prove itself first.”

In Washington, members of Congress are sounding the alarm about a Russian spy ship that was sailing off the Connecticut coast on Wednesday. They said the vessel, the Viktor Leonov, may have been collecting information on Naval Submarine Base New London, the U.S. Navy’s main submarine facility on the East Coast and home port for 15 nuclear subs, CBS News correspondent Don Dahler reports.

The U.S. ceased military-to-military relations with Russia in the wake of Moscow’s 2014 annexation of Ukraine’s Crimea region. But last year, the Obama administration considered plans to cooperate militarily with Russia as part of a cease-fire deal in Syria.

Senior Defense Department leaders opposed the plan, and it quickly fell apart as the cease-fire collapsed.

Also Thursday, Secretary of State Rex Tillerson met with Russian Foreign Minister Sergey Lavrov in the highest-level face-to-face contact between the two countries since Mr. Trump took office. Lavrov was asked if Russia is concerned about turmoil in the Trump administration. He repeated Moscow’s standard line that Russia “does not interfere in the domestic matters of other countries.”

After the meeting on the sidelines of a conference of foreign ministers of Group of 20 major powers in Bonn, Germany, Tillerson said that Russia must abide by a 2015 deal aimed at ending fighting between Ukrainian forces and Russia-backed separatists.

“As we search for new common ground, we expect Russia to honor its commitments to the Minsk agreements and work to de-escalate the violence in the Ukraine,” Tillerson said.