Russia attacks Ukraine

United Nations Secretary General Antonio Guterres told Russian President Vladimir Putin to stop "attacking Ukraine" and to give peace a chance, speaking at an emergency UN Security Council meeting on Wednesday night.

“The day was full of rumors and indications of an offensive against Ukraine was imminent. In the recent past, there were several situations with similar indications, similar rumors. And I never believed in them, convinced that nothing serious would happen,” Guterres told the council. “I was wrong. And I would like not to be wrong again today.”

The US Ambassador to the United Nations on Wednesday night called on Russia to “back away from the brink, before it is too late.”

Thomas-Greenfield said she had spoken to US President Joe Biden prior to the meeting, and he asked her “to convey in the strongest possible terms his — and our — steadfast support for Ukraine, and support for the urgent meeting this Council has convened tonight.”

“Furthermore, he asked me to share that the United States and our allies and partners will continue to respond to Russia’s actions with unity, with clarity, and with conviction,” she said.

State Department spokesperson Ned Price on Wednesday night reiterated US warnings about potential Russian false flags that Moscow could use to justify an invasion. 

“Beware of the following Kremlin disinformation campaigns seeking to justify military action - no evidence supports any of these false claims," Price tweeted.

Read the tweet:

The United States has terminated waivers and imposed sanctions on Nord Stream 2 AG — the parent company of the Nord Stream 2 gas pipeline — and its top executives, US Secretary of State Antony Blinken said in a statement Wednesday night.

US President Joe Biden said earlier in the day he had authorized the sanctions “in response to Russia’s actions in Ukraine.” 

The waivers: Last year, the Biden administration waived the sanctions on the company behind the controversial gas pipeline between Russia and Germany, claiming “it was in the national interests of the United States.”

However, Blinken said Wednesday that following Russia’s actions this week, those waivers were no longer in the US' national interest. The newly imposed sanctions and visa restrictions target the company, its CEO Matthias Warnig, and its corporate officers.

Russian state news reported on Thursday that Ukrainian security forces have shelled the pro-Moscow region of Donetsk in eastern Ukraine, citing reports from the Donetsk People's Republic representative office in the Joint Center for Control and Coordination of the Ceasefire Regime (JCCC).

State news agency RIA-Novosti quoted the report as saying the shelling was in the direction of the village of the Trudovskaya mine, on the outskirts of Donetsk, at 2:40 a.m. Ten 120mm mortars had been fired, heavy weapons that are prohibited by the Minsk agreements, according to the reports.

Russian state television also reported heavy fire in separatist-held parts of eastern Ukraine. CNN could not immediately verify those reports.

The US State Department has warned that Russia may use so-called false flags, including claims that Ukraine is attacking Donetsk, to justify an invasion. 

Some background: The 2015 Minsk agreement was hammered out in the Belarusian capital in a bid to end what was then a bloody 10-month conflict in eastern Ukraine. But it has never been fully implemented, with its key issues still unresolved.

It was was signed by representatives of Russia, Ukraine, the separatist leaders and the Organization for Security and Co-operation in Europe (OSCE). It was subsequently endorsed by a UN Security Council resolution. This put an end to the worst of the fighting at the time.

Key Ukrainian government websites were down early Thursday local time following a day in which Ukrainian agencies dealt with multiple cyberattacks and as concerns mounted over Russian troop movement into Ukraine's separatist regions.  

The websites of the Ukrainian Cabinet of Ministers, and those of the ministries of foreign affairs, infrastructure, education and others, were experiencing disruptions.

In a separate and potentially more serious hacking incident hours earlier, a data-wiping tool was found on hundreds of computers in Ukraine, according to cybersecurity researchers, raising concerns that a destructive cyberattack was unfolding amid Russia's military escalation.

The recruitment center of Ukraine's Territorial Defense Force across the street from Kyiv's town hall was buzzing with activity on Wednesday.

At one point, volunteers were queuing to sign up. The branch of Ukraine’s armed forces is comprised mostly of civilian volunteers who receive military training and are charged with protecting key sites.

The force has recently started a massive recruitment push. Posters asking people to sign up are displayed on Kyiv’s metro and elsewhere across the city, with a big campaign on social media.

Leonid Atamasiev, a 46-year old tech worker, was one of those visiting to sign up after learning about the recruitment center online.

Atamasiev said he has never been in the military, but has worked as a volunteer in the past.

“I don’t know what I will do, but I am ready to do anything they need me to,” he said.

CNN's Frederik Pleitgen has witnessed what he describes as "a lot of very ominous movement" on the ground in Russia, near northeast Ukraine.

"The Russian military really [is] in a position where it certainly seems as though they could strike at any point in time," he added.

Meanwhile, further south, near Donetsk, Pleitgen noted other examples of assembled Russian military.

"You see a lot of Russian convoys there that seem to be forming," he said. "[It is] unclear whether or not they've gone over the border yet, the way that all of this could happen is, you might have two areas where the Russians might try to go across the border."

Pleitgen closed his live report by offering a statement on the general atmosphere in the region.

"You really feel how things are getting more tense here by the minute," noted Pleitgen, adding, "you certainly also see that the Russian military is on the ground here, and certainly at least seems to be in a position to be able to strike at any point in time if Vladimir Putin chooses to order that."

Russia has issued a notice banning civil aircraft from flight routes bordering north-eastern Ukraine.

Russia issued a NOTAM (notice to airmen or notice to air missions) that covers a corridor of territory where Russian forces have gathered over the past weeks.

The NOTAM remains in force until May 18.