BRUSSELS--European leaders appear ready to order new sanctions against Russia this weekend after accusations that Moscow has scaled up its military intervention in Ukraine.

The European Union's leaders originally were to just hold a brief discussion on Ukraine on Saturday evening at a Brussels summit to pick the EU's new foreign policy chief and fill another top job. However, the mood in the bloc shifted over the last 48 hours following western accusations that Russia has sent hundreds of troops into Ukraine along with equipment to bolster pro-Moscow rebels in eastern Ukraine.

At an EU foreign ministers' meeting in Milan on Friday, several ministers accused Russia of staging an invasion of Ukraine.

This is "the second Russian invasion of Ukraine within the year," Swedish Foreign Minister Carl Bildt said.

Lithuanian Foreign Minister Linas Linkevicius said it is time for the EU to consider offering military support to Ukraine in addition to stepping up sanctions against Moscow. Ukrainian President Petro Poroshenko, who will join Saturday's EU leaders meeting, has been pleading for western military assistance. Ukraine isn't a member of the EU.

"We have to consider all possible support to the Ukrainian government because they are facing incursion, invasion, aggression from outside," Mr. Linkevicius said.

In Germany, where officials had been skeptical of additional sanctions for fear of derailing talks between Moscow and Kiev, the tone shifted markedly in recent days. A renewed diplomatic push led by Berlin, including a two-hour meeting between Russian President Vladimir Putin and Mr. Poroshenko in Belarus, appears to have failed, officials acknowledged.

Last Saturday, on a visit to Kiev, German Chancellor Angela Merkel said new sanctions against Russia weren't on her agenda. But Thursday, she said European leaders would need to consider new measures in Brussels.

On Friday, Ms. Merkel's foreign minister, Frank-Walter Steinmeier, warned the situation was increasingly spiraling out of control, with the risk of a direct military confrontation between Russia and Ukraine increasing.

"All the hopes that we had that the conversation between President Poroshenko and President Putin would help calm the situation have been dashed," he said.

In the German parliament, support built for sanctions. Ms. Merkel's conservative bloc issued a statement Friday from Deputy Chairman Andreas Schockenhoff, describing Russian troops entering Ukraine as a "warlike act."

"I think it came a little bit as a shock that at the very moment Putin shook hands with Poroshenko [in Minsk], he moved toward more open Russian direct involvement in Ukraine," said Ulrich Speck, visiting scholar at Carnegie Europe. He said this may be the end of the "illusion" that diplomacy can work.

French Foreign Minister Laurent Fabius on Friday confirmed that "if Russia doesn't change its behavior, it's probable that sanctions will be reinforced."

The U.S. and other Western allies have called on Paris to call off its plans to deliver the first of two warships to Russia in the fall. But France has refused to cancel the contract, saying such a move would be too costly. On Friday, Mr. Fabius didn't address the matter during his televised remarks.

Meanwhile, European Commission President José Manuel Barroso spoke with Mr. Putin on Friday in what a spokeswoman called a "very frank" conversation.

On Thursday, the North Atlantic Treaty Organization asserted that well over 1,000 Russian troops are operating in eastern Ukraine, deployed to prevent the collapse of Russian separatists after Ukrainian forces were closing in.

The Kremlin denies that any Russian troops have been deployed in Ukraine and say the handful that Kiev has captured were there "by accident" and should be returned.

EU diplomats said it was unlikely that the leaders will decide on specific sanctions measures at Saturday's meeting. Instead, said a number of officials, they are likely to order Brussels officials to draw up further steps in the coming days.

In July, the EU agreed for the first time on broad sanctions against Russia's economy, the sharpest measures yet since Moscow annexed Crimea in March. At the time, the bloc said the measures could be scaled up or down according to developments.

July's sanctions included a ban on purchasing newly issued bonds and shares in five Russian majority state-owned banks. The EU agreed on an arms embargo and a ban on the sale of dual-use goods to military end-users in Russia. The bloc also agreed to stop exports of high-end technology to be used in deep-water oil exploration and production.

Still, the measures included a number of exemptions, including permitting the completion of defense contracts already signed, like France's sale of the Mistral warship.

At present, there are no detailed options for further steps, officials said Friday. However the sanctions could be expanded to include additional Russian banks, other high-tech equipment for the energy sector or to further stem exports of dual use goods. EU officials said there is little appetite now for canceling existing defense contracts or curtailing EU energy imports from Russia.

U.K. officials said Friday the EU should take steps to further align the bloc's sanctions with U.S. restrictions, including on defense exports and sales of high-end technology.

"I think we are far from the ceiling of the sanctions that the EU could put in place," said one official.

Since July's sanctions steps, several EU leaders have questioned the wisdom of economic restrictions, including the Slovak and Hungarian prime ministers. On Friday, officials from both countries said that given Russia's steps in recent days, neither government is likely to block further EU steps.

After last month's EU sanctions, Russia imposed a ban on many EU and U.S. agricultural products.

Arriving at Friday's meeting in Milan, Polish Foreign Minister Radoslaw Sikorski handed out Polish apples--banned by Moscow--to reporters.

"President Putin says they are poisonous but I assure you they are very good," Mr. Sikorski said.

Nicholas Winning in London, Greg White in Moscow and Naftali Bendavid in Brussels contributed to this article.

Write to Laurence Norman at laurence.norman@wsj.com and Anton Troianovski at anton.troianovski@wsj.com

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