Rebel leaders in eastern Ukraine have asked Russia for military assistance to fend off the Ukrainian “aggression”, the Kremlin has said.

The appeal raises the prospect of Russia’s direct military involvement in eastern Ukraine amid Western fears that Moscow is poised to launch an all-out invasion of its neighbour.

Kremlin spokesman Dmitry Peskov said the rebel chiefs wrote to President Vladimir Putin, pleading with him to intervene after Ukrainian shelling caused civilian deaths and crippled vital infrastructure.

The move comes after Mr Putin recognised the independence of Russia-backed rebel regions in eastern Ukraine and signed friendship treaties with them.

On Tuesday, politicians gave Mr Putin permission to use military forces outside the country.

White House press secretary Jen Psaki said the separatists’ request for Russian help was an example of the sort of “false-flag” operation that the West had warned Moscow would use to create a pretext for war.

“So we’ll continue to call out what we see as false-flag operations or efforts to spread misinformation about what the actual status is on the ground,” she said.

In Ukraine, politicians approved President Volodymyr Zelensky’s decree that imposes the measure for 30 days starting Thursday. The state of emergency allows authorities to impose curfews and restrictions on movement, block rallies and ban political parties and organizations “in the interests of national security and public order.”

The action reflected the increasing concern by Ukrainian authorities after weeks of trying to project calm.

The Foreign Ministry advised against travel to Russia and recommended any Ukrainians there to leave immediately, saying Moscow’s “aggression” could lead to a significant reduction in consular services.

“For a long time we refrained from declaring a state of emergency … but today the situation has become more complicated,“ National Security and Defence Council head Oleksiy Danilov told the parliament, emphasising that Moscow’s efforts to destabilise Ukraine represented the main threat.

Ukrainian authorities have repeatedly voiced concern that pro-Russian groups inside the country could try to destabilize it, including a pro-Moscow political party represented in parliament.

The introduction of the state of emergency follows Mr Putin’s move on Monday to recognise the independence of rebel regions in eastern Ukraine, where a nearly eight-year conflict has killed over 14,000 people.

Mr Putin has sanctioned the deployment of Russian troops there to “maintain peace”.

Russia on Wednesday evacuated its embassy in Kyiv as hopes for a diplomatic way out of a new, potentially devastating war in Europe waned.

The US and key European allies accused Moscow of crossing a red line Tuesday in rolling over Ukraine’s border into separatist eastern regions known as the Donbas, with some calling it an invasion.

Pentagon press secretary John Kirby said the Russian force of more than 150,000 troops arrayed along Ukraine’s borders is in an advanced state of readiness.

“They are ready to go right now,” Mr Kirby said.

In response to Russia’s action, President Joe Biden allowed sanctions to move forward against the company that built the Russia-to-Germany Nord Stream 2 gas pipeline and against the company’s chief executive.

“Today, I have directed my administration to impose sanctions on Nord Stream 2 AG and its corporate officers,” Mr Biden said in a statement.

“As I have made clear, we will not hesitate to take further steps if Russia continues to escalate.”

Germany said it was indefinitely suspending the project, after Mr Biden charged that Mr Putin had launched “the beginning of a Russian invasion of Ukraine” by sending troops into the separatist regions of eastern Ukraine.

The pipeline is complete but has not yet begun operating.

Mr Biden waived sanctions last year against Nord Stream 2 AG, when the project was almost completed, in return for an agreement from Germany to take action against Russia if it used gas as a weapon or attacked Ukraine.

Mr Putin said on Tuesday he had not yet sent any Russian troops into the rebel regions contrary to Western claims, and Donetsk rebel leader Denis Pushilin insisted on Wednesday there were no Russian troops in the region even though a local council member claimed the previous day they had moved in.

Ukraine’s Minister for Digital Transformation Mykhailo Fedorov said a wave of denial-of-service attacks targeted official websites and some banks on Wednesday, knocking sites of the parliament, cabinet and Foreign Ministry offline and causing interruptions or delays to the sites of the defense and interior ministry, which controls the police.

Many of the same sites were similarly knocked offline in attacks last week that the US and UK governments quickly blamed on Russia’s GRU military intelligence agency.

Such attacks barrage websites with junk traffic, rendering them unreachable.

Wednesday’s DDoS attacks appeared to have less impact than the earlier onslaught, with targeted sites soon reachable again as emergency responders blunted them.

These were just the latest in a series of signs of escalating tensions.

Kyiv recalled its ambassador to Russia and considered breaking all diplomatic ties with Moscow; dozens of nations further squeezed Russian oligarchs and banks out of international markets; the US repositioned additional troops to Nato’s eastern flank bordering Russia; and the top US diplomat cancelled a meeting with his Russian counterpart.

Already, the threat of war has shredded Ukraine’s economy and raised the spectre of massive casualties, energy shortages across Europe and global economic chaos.

Even as the conflict took a new, dangerous turn, leaders warned it could still get worse.

Mr Putin has yet to unleash the force of the 150,000 troops massed on three sides of Ukraine, while Biden held back on even tougher sanctions that could cause economic turmoil for Russia but said they would go ahead if there is further aggression.