"The politically motivated proceedings against Alexei Navalny and against numerous other critics of the Russian government, and the inhumane prison conditions, show how brutally the Russian judiciary is cracking down on dissenters and the means President (Vladimir) Putin is using to suppress freedom of expression in Russia," the spokeswoman said.

EU foreign ministers were meeting Navalny's widow on Monday to send a "message of support" to Kremlin opponents after his death in jail, the bloc's top diplomat said.

"We have to send a message of support to the Russian opposition," EU foreign policy chief Josep Borrell told journalists.

Yulia Navalnaya was to join ministers of the 27-nation European Union in Brussels, as they weigh their -- limited -- options for inflicting new costs on Russian President Vladimir Putin.

Navalny's death in an Arctic prison last week has shocked the country's exiled opposition which -- along with the West -- pointed the finger at the Kremlin.

The EU has already imposed unprecedented sanctions on Moscow -- including on Putin -- over its invasion of Ukraine and officials concede it will be difficult to impose further major pain after Navalny's death.

But Borrell said he expected EU member states to propose fresh sanctions on those directly responsible for Navalny's treatment, including in Russia's prison system.

"The great responsible is Putin himself," Borrell said.

He said that Brussels would look to rename its global human rights sanctions blacklist after Navalny in a symbolic move.

German Foreign Minister Annalena Baerbock said ministers would "initiate further sanctions measures" over Navalny's death.

"The Russian brutal war of aggression... is not just a war against Ukraine, but against freedom itself," she said.

Other ministers said the death of Putin's greatest domestic foe should serve to bolster backing for Kyiv as its outgunned forces struggle to hold back Russia.

"Putin is a murderer. Putin has murdered one person who fought for freedom for democracy, and this is exactly why we have to keep going," said Estonian Foreign Minister Margus Tsahkna.

"The most clear response would be if we finally do our job. We have to support Ukraine."

That was echoed by Belgian minister Hadja Lahbib who warned that the death of Navalny served to underline the threat the Kremlin poses as it presses its offensive of Ukraine.

"We must be aware of what is at stake today," she said.

"If Russia manages to expand, it is a dictatorship that will expand and move a little closer to the European Union."

Meanwhile, the Kremlin said Monday the investigation into the death of Alexei Navalny was ongoing as it slammed "vulgar statements" over the Kremlin's responsibility for his death.

"It's ongoing, all the necessary actions are being carried out," Kremlin spokesman Dmitry Peskov told reporters when asked about the investigation, adding that Moscow considered a series of "blatantly vulgar statements" about Navalny's death to be "absolutely unacceptable".