NATO on Wednesday said it is bracing for a "major offensive" by Russian forces in eastern Ukraine just one week after Moscow said it would withdraw forces from around the capital. 

"We see that Russia is moving forces out of the north to re-enforce them, to re-supply them, to re-arm them, and then to move them into the east where we are expecting a major offensive," Secretary-General Jens Stoltenberg told reporters. "President Putin's aim is to try to control the whole of Donbas and to establish a landbridge."

A resident looks for belongings in an apartment building destroyed during fighting between Ukrainian and Russian forces in Borodyanka, Ukraine, on Tuesday. (AP/Vadim Ghirda)

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The NATO chief said security officials have not seen any indication that Russian President Vladimir Putin has changed his ambitions to control all of Ukraine, despite claims from Moscow that it would divert troops amid peace talks with Kyiv.

Russian negotiators said last week that the Kremlin would move soldiers from Kyiv and the northern city of Chernihiv to "increase mutual trust."

But following the removal of Russian troops from Bucha, a suburb of Kyiv, hundreds of civilians were reported to have been found lying dead in the streets – some appearing to have been executed with their hands bound.

"We need to be prepared for a long haul," Stoltenberg said ahead of Wednesday’s meeting with NATO foreign ministers in Brussels, including Ukrainian Foreign Minister Dmytro Kuleba and U.S. Secretary of State Antony Blinken. 

A body with hands bound by white cloth, who according to residents was shot by Russian soldiers, lies in the street in Bucha, Ukraine, on Sunday. (Reuters/Zohra Bensemra)

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Stoltenberg said NATO will be looking to establish a "new strategic concept" to strengthen NATO’s force posture in Europe and to increase support for Ukraine. 

The NATO leader called on all member nations to not only strengthen economic sanctions on Moscow, but to increase the amount of military support being provided to Ukraine. 

"Ukraine has an urgent need for military support. And that's the reason why it is so important that NATO allies agree to further support Ukraine with many different types of military equipment," the secretary-general said.

Stoltenberg warned the international community that the war in Ukraine could last for months if not years.

A dog and Ukrainian army soldiers in the street on the outskirts of Kyiv.

A dog is seen in the middle of a street as Ukrainian army soldiers take part of a military sweep to search for possible remnants of Russian troops after their withdrawal from villages in the outskirts of Kyiv, Ukraine, Friday, April 1, 2022.  ((AP Photo/Rodrigo Abd))

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"Regardless of when the war ends, this has long-term implications for our security," he continued. "Because we have seen the brutality, we have seen the willingness by President Putin to use military force to reach his objectives. 

"And that has changed the security reality in Europe for many, many years," Stoltenberg added.