NATO chief Jens Stoltenberg has said that Russia is readying for a "full-fledged attack" on Ukraine.
Speaking to the German broadcaster, ARD, Mr Stoltenberg said: "Every indication indicates that Russia is planning a full-fledged attack against Ukraine.
"We all agree that the risk of an attack is very high."
NATO has already begun to relocate staff from the capital of Ukraine, Kyiv, to Lviv in the west of the country and Brussels in Belgium for their safety.
An alliance official told AFP: "The safety of our personnel is paramount, so staff have been relocated to Lviv and Brussels," the official told AFP, without giving numbers.
"The NATO offices in Ukraine remain operational."
A number of other Western countries have already moved their diplomats from Kyiv to Lviv as they prepare for Russian military action.
The NATO official said: "NATO and allied countries are monitoring and assessing the situation very closely and continue to take all the necessary measures."
The news comes after US President Joe Biden said on Friday that he was "convinced" Russia would invade Ukraine this week.
However, Germany's foreign minister has warned the public about assuming Russia's decisions on Ukraine.
Minister Annalena Baerbock said: "We do not know yet if an attack has been decided on," but added that the "threat against Ukraine is very real".
Ms Baerbock made her remarks after hosting a G7 foreign ministers' meeting on the fringes of the Munich gathering.
The group of seven most developed nations, including the United States, reaffirmed that they were "united" in their support for Ukraine and determined to respond to any violation of its sovereignty.
Ukrainian President Volodymyr Zelensky also attempted to tone down President Biden's prediction saying: "We do not think that we need to panic."
Speaking on the main stage in Munich, Mr Zelensky said it was "difficult for me to judge" the US intelligence behind the warnings, but "I trust Ukrainian intelligence, who understand what's going on along our borders".
He added: "We need to preserve our stability. We need to keep calm and be adults."
Meanwhile, the Ukrainian ambassador to Ireland has urged Ireland to support "tough" sanctions against Russia should it launch an invasion.
Larysa Gerasko told RTÉ News: "We are grateful to Ireland for its unwavering support."
But warned the "whole world, including Ireland, has to act immediately" should Russia attack.
