Russia is staging helicopters, artillery systems and troops in preparation for what is expected to be a renewed offensive in the Donbas region of eastern Ukraine, a senior U.S. defense official said Wednesday.

Russian forces have been using the cities of Belgorod and Valuyki in Russia near Ukraine's northeast border as primary sites to stage equipment and resupply troops, the official said. The United States is now seeing a third Russian town, Rovenki, also near the Ukraine northeast border, being used for that purpose.

The official said there's already signs that Russian forces are on the move south to the Donbas region.

"We continue to see units flowing into the northern Luhansk Oblast, that north part of the Donbas," the official said. "They're flowing in from Valuyki and from that town called Rovenki."

The long Russian convoy is heading south and, at last check, was near the city of Izium in eastern Ukraine, according to the official.

Other Russian troops to the south of Izium appear to be working to improve their mobility and firepower in the region, the official said.

"We've seen them try to erect a temporary bridge over a local river," the official said. "They're increasing their artillery in the area."

-ABC News' Matt Seyler

In a brief moment of joy amidst the brutality of war, rescuers in eastern Ukraine on Wednesday pulled a puppy alive from the rubble of a bombed building, authorities said.

The rescue unfolded in Mykhailivka in the Donetsk region, according to the Donetsk Regional Police.

Police released a video showing rescuers digging through the rubble with bare hands to reach the trapped pooch. Rescuers said they heard the puppy whining as they were picking through the rubble.

"Thanks to the boys for doing everything quickly and promptly here," said the dog’s owner while holding the trembling puppy in his arms

Finland and Sweden -- both traditionally militarily neutral countries -- are considering a dramatic pivot in their security policy following Russia's invasion of Ukraine.

Leaders of both countries publicly stated during a joint press conference Wednesday that they are considering taking steps to join the NATO alliance.

"The European security architecture has changed fundamentally after Russia's invasion of Ukraine," Finland's Prime Minister Sanna Marin said. "The change in the security landscape makes it necessary to analyze how we best secure peace for Finland and in our region in the future."

Swedish Prime Minister Magdalena Andersson added, "We have to really think through what is best for Sweden and our security and our peace in this new situation and, of course, what is happening and the discussion in Finland is important for us to follow. Therefore, we need to have a very close contact, but we have to have a process in Sweden to think this through."

Last week, NATO Secretary-General Jens Stoltenberg said he's had close contact with political leaders of both countries and has conveyed that it's up to them whether to decide joining NATO.

"But if they apply, I expect that 30 allies will welcome them and that we will find ways to also address the concerns they may have about this interim period between (when) they have applied and until the last ratifications has taken place," Stoltenberg said.

Kremlin spokesperson Dmitry Peskov warned that further expansion of NATO to include Finland and Sweden will not contribute to security in Europe.

"In itself, the alliance is rather a tool sharpened for confrontation, this is not an alliance that ensures peace and stability," Peskov said, according to Russian state-run news agency TASS.

-ABC News' Christine Theodorou

About 1.4 million people have been left without clean running water in war-torn eastern Ukraine and an estimated 4.6 million people across the country are at risk of losing their supply, the United Nations Children's Fund reported Wednesday.

UNICEF officials said heavy fighting in eastern Ukraine, including the widespread use of explosive weapons in populated areas, has decimated a large part of the region's water systems. The agency tallied 20 separate incidents in which water infrastructure has been damaged or destroyed and warned of a "risk of complete collapse."

Damaged electrical grids have shut down water pumps and explosion-related damage to pipelines are disrupting the flow of water, according to UNICEF.

"Water is essential for life and a right for everyone," Osnat Lubrani, the U.N. resident coordinator in Ukraine, said in a statement. "The health risks, particularly for children and the elderly, caused by water stoppages are severe, as people are forced to use dirty water sources, resulting in diarrhoea and other deadly infectious diseases."

Murat Sahin, a UNICEF Ukraine representative, added that, “Young children who live in conflict zones are 20 times more likely to die from diarrheal diseases linked to unsafe water than from direct violence, as a result of war."

In hard-hit Mariupol, which has been under siege since the start of the Russian invasion on Feb. 24, thousands of residents trapped in the city are seeking any water they can find and resorting to dirty water sources, according to UNICEF. Major cities across the Donetsk and Luhansk regions are also cut off from water supplies.

The water systems in Sumy, Chernihiv and Kharkiv have also been seriously damaged, UNICEF said. An additional 340,000 people are at risk of losing their water supply from a reservoir in Horlivka in the Donetsk region that is inching closer to running dry, according to UNICEF.

Agency officials said that prior to the invasion, much of the water systems in eastern Ukraine were already ailing after eight years of a low-grade conflict in the region.

-ABC News' Christine Theodorou

White House national security advisor Jake Sullivan hinted Thursday of more sanctions coming against Russia in the "next week or two" aimed at targeting ways Moscow is evading sanctions already imposed.

“Where our focus will be over the course of the coming days is on evasion,” Sullivan said Thursday at the Economic Club of Washington. “As Russia tries to adjust to the fact that it’s under this massive economic pressure, what steps do they take to try to evade our sanctions and how do we crack down on that? And I think we'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond."

When Sullivan was asked whether sanctions will automatically be lifted if a negotiated peace deal between Russia and Ukraine is worked out, he appeared cautious with his words, saying, “a lot of that depends on what the shape and scope” of the agreement is.

“A lot of it depends on what the Ukrainians, in consultation with us and the Europeans come to agree to," Sullivan said. "You know, we're not going to do a deal over the head of the Ukrainians where we give a bunch of sanctions relief to Russia. But if some measure of sanctions relief were built in to some credible diplomatic solution led by the Ukrainians, that's something that we would happily discuss."

But Sullivan said Russian oligarchs shouldn't expect to ever get back their yachts and other assets seized under sanctions that have been imposed, saying the ultimate goal is "not to give them back” once the war is over.

“The president is actively looking at how we can deal with the fact that as we seize these assets, our goal is not to give them back. Our goal is to put them to a better use than that," Sullivan said. "But I'll be careful in what I say today because there's an ongoing kind of policy process around how we end up dealing with that question. But, rest assured, that the goal is not just to sit on them for a while."

-ABC News' Justin Gomez