By Laurence Norman and Valentina Pop 

BRUSSELS -- European Union leaders said early Friday that all options remained available if the Syrian and Russian bombing campaign against the northern Syrian city of Aleppo continues but backed off any threat of immediate action.

In a statement agreed after talks which ran past midnight, the leaders watered down their stance on the Aleppo attacks. An earlier threat that the EU could place sanctions on those supporting the Assad regime was removed from the text following opposition from Italy, among others, according to two senior officials.

Instead, leaders repeated what European politicians have been saying for days -- that "the EU is considering all available options, should the current atrocities continue."

The watered-down language suggests the EU is still some way from a point where it would start increasing pressure on Russia over the Syria conflict despite increasingly vocal public criticism of the Kremlin's air attacks, alongside the Assad regime, on rebel-held eastern Aleppo.

"We must show a robust and united European stance in the face of Russian aggression," U.K. Prime Minister Theresa May said as she arrived at her first EU summit. "We must continue to work together...to continue to put pressure on Russia to stop its appalling atrocities, its sickening atrocities in Syria."

German Chancellor Angela Merkel, who held talks on Syria on Wednesday night in Berlin with Russian President Vladimir Putin and French President François Hollande, said the EU must "take a stand."

"It's important to talk to each other, but not just to talk for talk's sake," Ms. Merkel said. "I think we are able...to show that what happens in Aleppo with Russian support is totally inhuman for the people who live there."

There was never any expectation that a sanctions decision would be made on Thursday but EU officials had on Wednesday night circulated a draft statement with much stronger language including the threat of placing targeted sanctions on people and entities supporting the actions of the Assad regime.

According to diplomats however, a number of leaders were unhappy with the stronger sanctions threat and wanted it removed. A number of EU governments, including in Slovakia, Greece, Italy and Hungary have criticized the bloc's economic sanctions against Russia over the Ukraine conflict and have said they don't want to further escalate tensions.

Earlier this week, Russia announced that together with the Syrian government, it would suspend air attacks on the rebel-held east of Aleppo on Thursday. As the EU leaders gathered in Brussels, Russian Defense Minister Sergei Shoigu said the cease-fire would be extended 24 hours.

Moscow presented the plan as a way to relieve suffering in the city where Western leaders have said Russian warplanes, together with Syrian government forces, have targeted rebels and civilians.

Russia says it has given militants and civilians an opportunity to leave the city during the cease-fire. Russian officials have also said the humanitarian pause could spur new diplomacy around Syria following its collapse in the wake of the failure of a peace plan brokered by the U.S. and Russia.

Ms. Merkel reiterated calls for a long-lasting cease-fire, "not just one for a few hours a day," that would allow humanitarian aid to reach Aleppo.

Elsewhere in Brussels, Jens Stoltenberg, the North Atlantic Treaty Organization secretary-general, said he was concerned about the deployment of a Russian aircraft carrier to the Mediterranean possibly taking part in strikes on Aleppo.

Mr. Stoltenberg said the alliance navies will monitor the Russian ships as they travel to the Mediterranean.

"We are concerned that the Russian carrier group will support military operations in Syria in ways which will increase humanitarian and human suffering," Mr. Stoltenberg said.

On Monday, EU foreign ministers agreed to add more Syrian officials to their sanctions against the Assad regime. There are already more than 200 individuals and around 70 entities under the EU's Syria sanctions, including several Iranian targets. Some capitals have pushed for these targeted sanctions -- travel bans and asset freezes -- to be extended further to include Russian officials.

However European leaders said no decisions were possible Thursday. Swedish Prime Minister Stefan Löfven said ahead of the meeting that while sanctions are an option, "I don't think there's unity now."

French President François Hollande said he was focused on trying to ensure Russian and Syrian attacks on Aleppo don't resume.

"Today the priority is to extend the cease-fire," he said.

Meanwhile, Belgian officials summoned the Russian ambassador for a meeting Thursday morning, after Russian media accused Belgium of being responsible for an airstrike in the Syrian city of Aleppo that killed six civilians.

Belgian Foreign Minister Didier Reynders and Defense Minister Steven Vandeput said in a statement Wednesday that no Belgian aircraft were operating over Aleppo province and the accusations are "groundless and unsubstantiated."

A Belgian government spokesman said Belgium's position was conveyed clearly to the Russian envoy but didn't provide any further details of the meeting.

EU leaders had been due to discuss the future of their ties with Russia, following a request in June by Italian Prime Minister Matteo Renzi for such talks. Mr. Renzi wanted to see the bloc's engagement with Mr. Putin broadened and pressure eased.

However the mood has turned dramatically since the Russian attacks started on Aleppo and support for easing pressure on Moscow has largely evaporated.

--Thomas Grove, Natalia Drozdiak and Anton Troianovski contributed to this article.

Write to Laurence Norman at laurence.norman@wsj.com and Valentina Pop at valentina.pop@wsj.com

(END) Dow Jones Newswires

October 20, 2016 20:09 ET (00:09 GMT)