KYIV (AFP) - Up to 2 million people living along the front line in eastern Ukraine risk displacement if the festering conflict spirals, the Norwegian Refugee Council warned on Thursday (Feb 3), as tensions soar over Russia's military buildup.

"The lives and safety of millions of people in eastern Ukraine hang in the balance as we wait for a political breakthrough to the current impasse," Jan Egeland, Secretary General of the Norwegian Refugee Council (NRC), said in a statement after visiting the region.

"We must not underestimate the human suffering of renewed conflict - it would result in increased civilian casualties, massive displacement and soaring humanitarian needs."

Western leaders have sounded the alarm over a potential Russian invasion after Moscow deployed more than 100,000 troops to the border with Ukraine. The Kremlin denies it is planning an incursion.

Russia seized the Crimean peninsula from Kyiv in 2014 and has fuelled a simmering separatist conflict in the east of the country that has claimed more than 13,000 lives since then.

As tensions spike, the NRC warned that "up to two million people living in a 20-kilometre zone on both sides of the contact line in eastern Ukraine would be under increased threat of violence and displacement if the conflict escalates".

The organisation said that more than 850,000 people are already internally displaced and three million rely on humanitarian assistance.

"Active hostilities would dramatically worsen the existing humanitarian situation, where needs are already high from years of violence," it said.

The NRC said that any surge in the conflict could "reverse significant improvements" in recent years that have seen the number of people requiring assistance fall from five million in 2015.