BRUSSELS (BLOOMBERG, AFP, REUTERS) - Some European Union governments are pushing for the bloc to quickly impose new sanctions in response to multiple reports that Russian troops executed unarmed civilians in Ukrainian towns, according to diplomats familiar with the discussions.

The European Commission was already honing measures that would mostly focus on closing loopholes, strengthening existing actions - such as export controls on technology goods and fully sanctioning banks already cut off from the SWIFT global payments system - and expanding the list of sanctioned individuals.

Some EU nations argue there is now a trigger for the new penalties to be put in place with speed, with Ukrainian officials reporting evidence of war crimes committed by Russian troops in northern areas, according to a diplomat familiar with the discussions.

There is not yet consensus on all the details for a new package, or when to implement it, even as the bloc's executive arm seeks in the meantime to put forward a set of corrective measures as early as this week.

A small number of member states, including Germany, are opposed to sanctioning Russia's energy sector, its maritime trade and other key industries, and EU sanctions require unanimous support.

The question for EU members is what actions would spur a fresh and fuller set of sanctions. Some continue to argue such measures should only be explored if Russia were to use chemical weapons or capture a major city, three diplomats said, asking not to be identified as the discussions are private.

Other states say the reported events in places like Bucha, a town on the outskirts of Kyiv, are enough to warrant action. And one of the diplomats said even the fresh measures on the table were not enough given the extent of the potential war crimes.

Ukraine has accused Russian soldiers of killing unarmed civilians, with officials saying they found hundreds of bodies in Bucha after Russian troops left.

Mr Mykhailo Podolyak, an adviser to President Volodymyr Zelensky, posted several photos on Twitter of dead people, some with their hands tied behind their backs. Moscow hasn't commented on the accusation so far.

The Kremlin has said previously it was only targeting the military and key infrastructure. It comes as Russia shifts tactics in the war, redeploying troops away from the north after weeks of failure to make ground.

Instead its campaign is focusing on areas in the east, including the Donetsk and Luhansk regions of Donbass, and Mariupol, a port city that has already been under siege for weeks.

Odessa meantime was rocked by explosions early on Sunday. Russia fired high-precision missiles from ships and aircraft that struck an oil refinery and three storage facilities near the southwestern port city, Defence Ministry spokesman Igor Konashenkov said.

The organisation Human Rights Watch said on Sunday it had documented several cases of apparent war crimes committed by Russian forces, including summary executions.

"The cases we documented amount to unspeakable, deliberate cruelty and violence against Ukrainian civilians," said Mr Hugh Williamson, Europe and Central Asia director at Human Rights Watch. "Rape, murder, and other violent acts against people in the Russian forces' custody should be investigated as war crimes."

The US last month made a formal determination that Russian troops had committed war crimes.

At the time Secretary of State Antony Blinken said the US had seen "credible reports of indiscriminate attacks and attacks deliberately targeting civilians, as well as other atrocities".

President Joe Biden has said he considers Mr Vladimir Putin a war criminal.

Increasingly frustrated with the stance of their counterparts, several EU countries, including Lithuania and Poland, have announced they will unilaterally stop importing Russian energy, while Estonia has put forward a proposal to withhold and freeze a share of Russia's energy revenue that it says could be an initial compromise.

One of the diplomats said the hope was the unilateral moves would lead to an agreement among all member states to do more in order to avoid risking damage to the EU's united front.

In a related development, Germany on Sunday condemned the killings of civilians in the Ukrainian town of Bucha as a "terrible war crime" and called for fresh EU sanctions against Russia.

"This terrible war crime cannot go unanswered," Mr Robert Habeck, Vice-Chancellor and Economy Minister, told German newspaper Bild the day after the bodies of nearly 300 civilians were found in mass graves after Russian troops withdrew, local Ukrainian officials said.

"I think that a strengthening of sanctions is called for. That's what we are preparing with our EU partners," Mr Habeck added.

German Foreign Minister Annalena Baerbock said the images from Bucha were "unbearable".

"Putin's frantic violence is wiping out innocent families and knows no bounds," she wrote on Twitter, adding that those responsible for war crimes must be held to account.

"We will strengthen the sanctions against Russia and further support the defence of Ukraine," the minister said.

Ukraine's Foreign Minister Dmytro Kuleba called Bucha a "deliberate massacre" and urged G-7 countries to impose "devastating" sanctions immediately.

Separately, Britain's Foreign Minister said on Sunday that as evidence mounts of "appalling acts" in the Ukrainian towns of Irpin and Bucha, Russia's attacks on civilians must be investigated as war crimes.

Foreign Secretary Liz Truss said in a statement that the government is seeing "increasing evidence of appalling acts by the invading forces in towns such as Irpin and Bucha", close to Kyiv.

Ms Truss said that Russian troops' "indiscriminate attacks against innocent civilians during Russia's illegal and unjustified invasion of Ukraine must be investigated as war crimes".

"We will not allow Russia to cover up their involvement in these atrocities through cynical disinformation," Ms Truss said, adding that the UK "will fully support any investigations by the International Criminal Court".

She also called for harsher sanctions, after Prime Minister Boris Johnson tweeted late on Saturday that the UK would "continue to step up military, economic and diplomatic support, including further ramping up sanctions".

Ms Truss said it was essential that the international community "continues to provide Ukraine with the humanitarian and military support it so dearly needs, and that we step up sanctions to cut off funding for Putin's war machine at source".

In more condemnation, EU chief Charles Michel on Sunday pledged further sanctions on Moscow as he slammed "atrocities" carried out by Russian forces near Ukraine's capital Kyiv.

"Shocked by haunting images of atrocities committed by Russian army in Kyiv liberated region #BuchaMassacre," European Council head Michel wrote on Twitter.

"EU is assisting Ukraine & NGO's in gathering of necessary evidence for pursuit in international courts."

Mr Michel added that "further EU sanctions & support are on their way".

Evidence has emerged of possible civilian killings around Kyiv as the Russian army has pulled back in the face of ferocious resistance from Ukrainian forces.