Russian President Vladimir Putin said Tuesday that military exercises and other moves by the West and Ukraine threaten Russia's security, warning against crossing the Kremlin's "red lines".

Addressing an investor conference via video link, Putin declined to say whether Moscow planned to move troops across Ukraine's border -- as the West has been alleging for weeks. 

"Look, they spoke about a possible Russian military intervention in Ukraine at the beginning of the year. But as you see this did not happen," Putin said.

"It is not about intervening or not intervening, fighting or not fighting. It's about mending ties," Putin said, adding that it was important to take into account the security interests of all parties. "If we sincerely strive to achieve this then no one will feel threatened."

Putin addressed investors as tensions spiral between Moscow and Brussels, and NATO looks to counter a fresh Russian military buildup on Ukraine's border. 

The new buildup follows a similar surge in the spring, when Russia gathered around 100,000 troops on Ukraine's borders but later announced a drawdown.

Putin said Moscow was concerned by Western moves to conduct large-scale previously unannounced military drills near Russia's borders, singling out US-led exercises in the Black Sea.

Separately, Foreign Minister Sergei Lavrov lobbed a series of new accusations against Kiev and said Russia reserved the right to respond if its security was threatened.

"We simply don't have the right to exclude that the Kiev regime may embark on a military adventure. This all creates a direct threat to Russia's security," Lavrov told reporters, speaking alongside his Brazilian counterpart Carlos Franca.

"If the West is unable to contain Ukraine, but, on the contrary, will incite it, then of course, we will take all the necessary steps to ensure our reliable security."

Last week Ukranian President Volodymyr Zelensky said that Russia was sending "very dangerous" signals with troop movements on the border, warning that his military was ready to push back any offensive. 

Moscow, which seized Crimea from Ukraine in 2014 and backs separatists fighting Kiev, has strongly denied it is plotting an attack and blames NATO for fuelling tensions. 

The conflict in the east has claimed more than 13,000 lives since 2014.