Britain's defence minister said on Sunday he was ready to work with his new US counterpart but that Western nations could not treat Russia as an equal partner as Moscow was a strategic competitor.
Several appointments by US President-elect Donald Trump have suggested his administration could forge warmer relations with Russia's Vladimir Putin, worrying several European allies, especially in eastern Europe.
"I'm ready to work with the new Secretary of Defence Jim Mattis... to be strong against Russian aggression towards NATO, to de-escalate tensions with Moscow and as I said to continue to work with Russia on how we get towards a settlement in Syria," Michael Fallon told the BBC.
"That can't be treating Russia as an equal. Russia is a strategic competitor to us in the West and we have to understand that," he said.
Trump is expected to name the chief executive of Exxon Mobil Corp as secretary of state, a source told Reuters on Saturday, an appointment that would put in place an official with close ties to the Russian government.
Fallon also emphasised Britain's support for Saudi Arabia after foreign minister Boris Johnson told an audience that the Saudis, Iran and others were "puppeteering and playing proxy wars."
A spokeswoman for Prime Minister Theresa May said earlier in the week that Johnson's views did not reflect the government's position on Saudi Arabia and its role in the region.
On Sunday, Fallon emphasised support for the kingdom, which since March 2015 has led a coalition launching air strikes in support of the Yemeni government of Abd Rabbu Mansour al-Hadi against Houthi fighters, who are backed by troops loyal to ex-President Ali Abdullah Saleh.
"It (Saudi Arabia) is perfectly entitled to defend itself and it is also leading the coalition to restore the legitimate government of Yemen," Fallon said.