At a meeting of NATO members in Brussels Thursday, U.S. Secretary of Defense Jim Mattis ruled out any military collaboration between the United States and Russia because current conditions are not ideal.

“We are not in a position right now to collaborate on a military level,” Mattis said at a news conference at NATO headquarters. “But our political leaders will engage and try to find common ground.”

Relations between the two countries have reached their lowest point since the Cold War because of Moscow’s alleged meddling in last year’s U.S. elections and its continued aggressive actions in Ukraine.

Mattis said before any military cooperation takes place with Russia, it must “prove itself” able to comply with international law.

Mattis made his comments after Russian Defense Minister Sergei Shoigu said Moscow is “ready to restore cooperation with the Pentagon.”

U.S. President Donald Trump praised Russian leader Vladimir Putin during the U.S. presidential campaign and has done so since taking office.

And although the U.S. ceased cooperating with Russia in 2014 after it annexed Crimea from Ukraine, Trump has expressed interest in working with Russia again on issues of common interest such as the fight against Islamic State.

Mattis said at Thursday he did not think the fight against IS would end quickly, but added the U.S. would like to speed up the multinational campaign against the militant group.

When asked about possibly sending U.S. ground troops into Syria, Mattis said he has not had enough time in office to form a plan and wants to confer with allies before moving forward.

Top officials meet

Meanwhile, U.S. Joint Chiefs of Staff Chairman Gen. Joseph Dunford met with his Russian counterpart, Gen. Valeriy Gerasimov, in Azerbaijan Thursday to discuss the status of current U.S.-Russia military relations.

The Pentagon issued a statement after the meeting, saying the two countries agreed to “enhance communications” and “improve operational safety of military activities” to prevent crises and “avoid the risk of unintended incidents.”

On the diplomatic front, U.S. Secretary of State Rex Tillerson met in Germany with Russian Foreign Minister Sergei Lavrov for the first time and said afterward that Washington could collaborate with Moscow under certain circumstances.

“As we search for new common ground, we expect Russia to honor its commitment to the Minsk agreements and work to de-escalate violence in the Ukraine,” Tillerson said in Bonn, where foreign ministers of the G-20 nations are meeting.

Under the 2015 Minsk agreement, Ukraine, Russia and Russia-backed separatists agreed to end the crisis in Ukraine, beginning with the withdrawal of heavy weapons.

Earlier this week, Trump accepted the resignation of newly-appointed National Security Adviser Michael Flynn following reports Flynn misled the administration about conversations he had with Russian Ambassador Sergey Kislyak.

Several U.S. investigations are underway into alleged interference by Russian intelligence services in favor of Trump during last year’s U.S. presidential election. President Trump has dismissed the allegations as nonsense.

Putin reaches out

Putin, meanwhile, called for a restoration of ties Thursday between U.S. and Russian intelligence agencies to work on common problems.

“Restoring dialogue with the special services of the United States and other NATO members is in our mutual interest,” Putin said in a televised speech before Russia’s Federal Security Service.

Tillerson is attending his first G-20 meeting, hosted by German Foreign Minister Sigmar Gabriel, who has been a vocal critic some of Trump’s policies.

The G-20 countries account for about 85 percent of the world economy and two-thirds of the global population.

The Bonn meeting is a precursor to a G-20 summit scheduled for July in Hamburg in what may be the first time Trump meets Putin in person.