The US is considering sending arms to Ukraine after it was revealed at least 3,000 Russian troops are now stationed in the east of the country. Such a move would seriously increase the tension between Washington and Moscow.

Speaking at a joint press conference with Ukrainian President Petro Poroshenko, US Defence Secretary James Mattis said President Donald Trump was "actively reviewing" whether to send lethal weapons and reiterated that the US would stand by Ukraine.

Stopping short of a concrete promise to supply military hardware, Mattis said the US would continue to put pressure on Moscow over "aggressive behaviour" and its failure to abide by the Minsk ceasefire agreement, which was intended to end separatist violence.

"Despite Russia's denials, we know they are seeking to redraw international borders by force, undermining the sovereign and free nations of Europe," Mattis told reporters.

The US has supported Ukraine since a pro-Western government took power after massive street protests in 2014. The resulting conflict between Ukrainian troops and Russian-backed militias led to the formal annexation of Crimea by Russia and the deaths of more than 10,000 people.

Despite repeated requests, the Obama administration shied away from sending weapons to the country, and during the US election campaign last year, Trump "stoked fears in Kiev he might mend ties with Moscow at Ukraine's expense", suggesting Crimea is a legitimate part of Russia, says the Daily Express.

These fears were "heightened following the release of a report which claimed North Korea's recent successful missile tests were only possible with the black market purchase of powerful rocket engines from a Ukrainian factory", the paper adds.

However, if Trump had hoped to mend ties with Russia, "his first few months in office have not seen a rapprochement", says Newsweek.

The latest snub to Russian President Vladimir Putin comes as Russia prepares to mount what could be one of its biggest military exercises since the cold war.

Western officials and analysts estimate that up to 100,000 military personnel could take part in the Zapad (West) 17 exercise, which will take place next month in Belarus, Kaliningrad and Russia. It will be "a display of power that will be watched warily by Nato against a backdrop of east-west tensions", says The Guardian.

Earlier this year, The Independent reported scores of tanks and other US fighting vehicles landed in Germany on their way to take part in Operation Atlantic Resolve, "which foresees the continuous presence of an American armoured brigade combat team in Europe on a nine-month rotational basis".

The mission represents the biggest transfer of American armour to the region since the fall of the Soviet Union, it says, and "was meant to help allay concerns held by Estonia, Latvia, Lithuania, Poland and other Nato allies about Russia".