BRUSSELS -- European Union officials are considering designating pro-Russian separatists in eastern Ukraine “terrorists” as they prepare potential fresh sanctions against Moscow over its role in the Ukraine crisis, diplomatic sources in Brussels say.

The addition of Ukraine’s self-styled breakaway “people’s republics” of Donetsk and Luhansk to the EU’s list of designated terrorist organizations is “under serious consideration,” according to two EU diplomats.

While the move is mainly symbolic, it would subject the rebel group to asset freezes and prohibit them from accessing financial services -- such as bank accounts -- in the bloc’s member states. The asset freezes have in sense already occurred, however, since the self-proclaimed leaders of the two separatist regions are already on the EU's asset freeze/visa ban list.

The two rebel groups, which Western governments accuse Russia of supporting, could be slapped with the designation as part of a new round of sanctions targeting Moscow and that are likely to be adopted by EU leaders at a summit in Brussels next month.

EU foreign ministers are set to meet on January 29 in Brussels to make recommendations for the package of punitive measures to be considered at the summit.

Several EU diplomats told RFE/RL that these measures will almost certainly include additions to a list of individuals hit with EU visa bans and asset freezes aimed at pressuring Moscow to exert its influence over the rebels to halt the bloodshed in eastern Ukraine.

The push for new sanctions against Russia comes amid escalating violence in the conflict, including the January 24 shelling of the Ukrainian city of Mariupol that officials say killed 30 people and wounded dozens more.

The United Nations says the rocket attacks originated from areas controlled by the separatists and deliberately targeted civilian areas, in violation of international law. The rebels, meanwhile, have accused Kyiv of carrying out the bombing, although Aleksandr Zakharchenko, the head of the self-proclaimed Donetsk People's Republic, said on January 24 that the separatists had launched an attack on Mariupol.

The EU heads of state issued a statement on January 27 condemning the Mariupol attacks and noting “evidence of continued and growing support given to the separatists by Russia.” The Kremlin has repeatedly denied backing the rebels.

In light of the “worsening situation,” the EU leaders asked their foreign ministers to consider “further restrictive measures” aimed at ending the fighting.

SWIFT ‘Nuclear Option’

EU foreign ministers this week could propose sanctions targeting Russia’s oil and financial sectors, including excluding Russian banks from the Belgium-based SWIFT payment system, the main global bank-transaction network, several EU diplomats told RFE/RL.

Speaking on January 27, Russian Prime Minister Dmitry Medvedev vowed vigorous countermeasures should Russia be cut off from SWIFT, saying Moscow’s response to such a move would have “no limits.”

But securing consensus among the EU’s 28 member states on a new round of broad economic sanctions will be difficult given a new Russia-friendly government in Greece and other EU countries wary of imposing harsher measures on Moscow, diplomatic sources in Brussels say.

The office of new Greek Prime Minister Alexis Tsipras issued a January 27 statement saying it did not agree with the EU leaders’ statement calling for further sanctions against Russia and complaining that it had not been consulted about the communique.

U.S. Assistant Secretary of State Victoria Nuland, meanwhile, said Washington is looking to work in coordination with the EU to ramp up sanctions against the Kremlin.

“We’ve looked at the sectors where Russia needs us most -- the high-tech energy sector, the defense trade, access to credit,” Nuland said in Washington on January 17. “There are more things that we can do along those lines. We are looking at that question now, along with Europe.”

A U.S. congressional source tells RFE/RL that any new sanctions levied by U.S. President Barack Obama’s administration and the EU are likely to mirror each other.

“It’s a question of who goes first,” the source said on condition of anonymity.

Both the United States and the EU have imposed several rounds of sanctions against Russian officials, wealthy business people, and companies, as well as certain restrictions targeting major players in Russia’s energy, defense, and financial sectors.

The punitive measures came last year in response to the Kremlin’s annexation of Ukraine’s Crimea Peninsula and its alleged support for the rebels in eastern Ukraine, where more than 5,000 people have died since the armed conflict erupted there in April, according to the UN.

Excluding Russia from SWIFT is a “nuclear option” that would be considerably more difficult than a similar measure targeting Iranian banks given that “Russia is an order of magnitude more integrated into the global economy than Iran,” the U.S. congressional source adds.

Speaking in New Delhi on January 25, Obama said the United States will "ratchet up the pressure on Russia" and "look at all additional options that are available to us, short of military confrontation, in trying to address" the uptick in violence in eastern Ukraine.

"We are deeply concerned about the latest break in the cease-fire and the aggression that these separatists -- with Russian backing, Russian equipment, Russian financing, Russian training, and Russian troops -- are conducting," he said.

Separatists Or Terrorists?

Should the EU add the self-styled “people’s republics” of Donetsk and Luhansk to its terrorist list as part of a new sanctions package, it would bring Brussels’ framing of the conflict closer to that of the Ukrainian government.

Kyiv has labeled its battle against the separatists an “antiterrorist operation” and accused the rebels of committing atrocities. Both Russia and the rebels, meanwhile, say the Ukrainian government is terrorizing its own citizens in the conflict after rising to power in what Moscow describes as a coup against former Ukrainian President Viktor Yanukovych last February.

The United Nations and rights groups like Amnesty International and Human Rights Watch have accused both sides of abuses, including torture and indiscriminate shelling of civilian areas.

An EU "terrorist" designation for the rebels would also mark a sharp reversal from the bloc's position on the matter voiced by its top foreign policy official last week.

Four days before the deadly shelling of Mariupol, Ukraine’s ambassador to the United States, Olexander Motsyk, asked EU foreign policy chief Frederica Mogherini in Washington whether Brussels would follow Kyiv’s lead in deeming the rebel groups terrorist organizations, which he compared to Islamic State militants.

Mogherini replied that the European Council had discussed this issue of how to define "the separatists" on "several" occasions.

"We’ve always come to the conclusion that it is not up to us to make such definitions,” Mogherini said at the January 20 event. "What is our role, and what I’ve tried to explain before, is to try and support your efforts for reaching a solution to the conflict."

With reporting by RFE/RL’s Luke Johnson in Washington, as well as AP, Bloomberg, and Interfax