The United States is not yet ready to cooperate militarily with Russia, Pentagon chief James Mattis said Thursday after Moscow's defence minister called for better ties.

"We are not in a position right now to collaborate on a military level, but our political leaders will engage and try to find common ground or a way forward," Mattis told reporters at a NATO summit in Brussels.

Russian Defence Minister Sergei Shoigu said earlier in Moscow that he was potentially "ready to restore cooperation with the Pentagon," and President Vladimir Putin called for Russian intelligence agencies to bolster contacts with US counterparts in the counter-terrorism fight.

The back-and-forth remarks come as President Donald Trump faces a crisis over ties between Russia and members of his campaign team.

The new president has repeatedly praised Putin and called for better cooperation with Russia, including in the fight against the Islamic State group in Syria.

But Mattis, a former Marine general, said Russia must first "prove itself" and follow international law before the US and NATO can consider closer military ties.

"The point about Russia is they have to live by international law just like we expect all nations on this planet to do," Mattis said.

Currently, the US-led coalition fighting IS in Syria and the Russian military, which is operating nearby in support of President Bashar al-Assad, do not cooperate but hold regular phone calls to avoid mid-air mishaps.

Mattis added he had "very little doubt" Moscow interfered in several elections, though he did not specifically mention the United States.

US intelligence agencies say the Russian government was involved in hacking Democratic Party communications and releasing files embarrassing to Trump's rival Hillary Clinton.

- 'Rock solid' commitment -

The new Pentagon chief's NATO visit, his first trip to Europe, was closely watched by jittery partners concerned over the potential Kremlin-White House ties and Trump's past comments showing disdain for the alliance.

Trump's national security adviser Michael Flynn was forced to quit this week over allegations he had discussed US sanctions with Russia's ambassador before taking office.

Mattis on Wednesday had issued a blunt warning to NATO, saying the 28-member alliance needed to meet earlier spending pledges or else America would "moderate" its commitment.

When asked for clarification, Mattis softened his language, saying the trans-Atlantic bond is "as strong as I've ever seen it."

He stressed America remained "rock solid" in its support of Article 5 -- NATO's core collective-defence tenet that says an attack on any member nation will be viewed as an attack on the whole alliance.

His comments come as the Chairman of the US Joint Chiefs of Staff Joe Dunford held talks with his Russian counterpart Valery Gerasimov in Azerbaijan and as new US Secretary of State Rex Tillerson met with his opposite number, Sergei Lavrov.

US, Russia military chiefs meet
Moscow (AFP) Feb 16, 2017 - The top military commanders from the US and Russia on Thursday held their first meeting since Donald Trump became president, as Moscow warned Washington against trying any strongarm tactics.

Chairman of the US Joint Chiefs of Staff Joe Dunford held talks with his Russian counterpart Valery Gerasimov in Azerbaijan's capital Baku, as both sides have mooted potential cooperation against Islamic State jihadists.

Russia's defence ministry said in a statement that the two generals "exchanged opinions regarding the condition of Russian-American relations" and on the security situation around the globe.

They also determined areas for cooperation in "increasing the security of military activity, decreasing tensions and the risks of accidents," the statement said.

Relations between Russia and the US have slumped to their lowest point since the Cold War over Moscow's meddling in Ukraine, and military ties are limited to a system aimed at avoiding clashes in the air over Syria.

Trump has repeatedly held out the prospect of cooperating with Russia in the fight against the Islamic State group, a goal that the Kremlin has long been pushing for.

The United States insisted, however, that Thursday's meeting between the military bosses was not political in nature and had been planned for months.

The talks took place as Trump's administration battles to fend off reports that aides had repeated contact with Russian intelligence during the presidential campaign last year.

Ahead of the meeting, Russia's defence minister also hit out at Washington with a warning not to try to negotiate with Moscow "from a position of strength"

"We are ready to restore cooperation with the Pentagon," minister Sergei Shoigu said in a statement.

"But attempts to build a dialogue from a position of strength in relation to Russia have no prospects."

Shoigu was responding to a comment to NATO by new Pentagon chief James Mattis on Wednesday in which he said Washington wanted to make sure its diplomats had the upper hand in any talks with Russia.

"We remain open to opportunities to restore a cooperative relationship with Moscow, while being realistic in our expectations and ensuring our diplomats negotiate from a position of strength," Mattis said in Brussels.