EU leaders also blamed Russia for the attack, but behind the scenes Europe was less united than it seemed.

The decision to recall the EU envoy to Moscow for one month came after British prime minister Theresa May told leaders at dinner that the Kremlin had tried to kill a former spy, Sergei Skripal, using a chemical weapon in England.

The attack "was part of a pattern of Russian aggression against Europe," she said.

One EU leader made the surprise proposal that member states should also expel Russian diplomats after London sent 23 of them packing earlier this month.

Diplomats declined to say who proposed the move, but France, Nordic countries, Baltic states, and Poland showed interest in taking the step. "All of us, we're considering such measures," Lithuanian president Dalia Grybauskaite told press.

Germany also threw its weight behind future EU sanctions over the Skripal incident.

"We are determined to react together, with the language we used here, but also possibly through additional measures," Merkel said, referring to the language of an EU statement adopted on Thursday.

The EU "agrees with the United Kingdom government's assessment that it is highly likely that the Russian Federation is responsible and that there is no plausible alternative explanation", the Thursday's communique said.

"Member states will coordinate on the consequences to be drawn in the light of the answers provided by the Russian authorities," it added.

It also promised future EU action on Russian "hybrid" threats, such as propaganda and cyber-attacks.

Some EU leaders voiced condemnation in even stronger terms.

"What occurred … was loathsome and reprehensible," Irish prime minister Leo Varadkar said.

EU sceptics

But behind the scenes, others had resisted blaming Russia in the joint statement, before eventually yielding as Thursday's talks overran.

Some even questioned the reliability of British intelligence, citing the fiasco of false British information in the Iraq war in 2003, diplomats said.

The EU sceptics included Austria, Belgium, Luxembourg, and Finland as well as Cyprus, Greece, and Italy in the south, sources said. Bulgaria, the Czech Republic, and Hungary also voiced doubt.

Greek leader Alexis Tsipras told press "we need to investigate" before blaming Russia.

The "information we've got so far is not enough to make decisions [on new sanctions]", Finnish prime minister Juha Sipila told the Bloomberg news agency.

Bulgaria's Boyko Borissov and the Czech Republic's Andrej Babis echoed that position.

"When we know who did it, then I'll comment. Who would say for sure now?", Borissov said. "Is there any evidence of this? I don't know, of course we trust our allies [the UK]," Babis said.

Belgium's Louis Michel called the question of Russia sanctions "very sensitive", adding: "It's important to keep a cool head, to keep calm".

Russia's line

The EU sceptics sounded a bit like Russia's line on Skripal.

British intelligence services had a "bad record of violating international law and misleading the international community … history shows that British statements must be verified", Russia's ambassador to the UK, Alexander Yakovenko, told press on Thursday.

Dmitry Peskov, the Kremlin spokesman, accused Britain of having an "unfriendly and provocative policy toward Russia".

Meanwhile, the UK's ambassador to Russia, Laurie Bristow, told international counterparts at an event in Moscow that Britain expelled the 23 Russian diplomats on security grounds, not for political reasons.

"The underlying point though here is that we were compelled to move to protect our national security … we have dismantled the network of Russian undeclared intelligence operatives working out of the diplomatic mission in the UK," he said.