Alexei Navalny's widow will meet European foreign ministers in Brussels on Monday, EU officials announced, as Brazilian President Luiz Inacio Lula da Silva cautioned against rushing to judgement over his death.

The 47-year-old Kremlin critic died in an Arctic prison on Friday after spending more than three years behind bars, prompting outrage and condemnation from Western leaders and his supporters.

EU foreign policy chief Josep Borrell said he would welcome Yulia Navalnaya to the bloc's Foreign Affairs Council on Monday.

"EU Ministers will send a strong message of support to freedom fighters in Russia" and "honour" Navalny's memory, he added on X, formerly Twitter, on Sunday.

Navalny was Russia's most prominent opposition leader and garnered a huge following as he campaigned against corruption under President Vladimir Putin.

In the hours following the announcement that her husband had died, Navalnaya, who had not seen him in two years, said she held Putin personally responsible.

She called on the international community to "unite and defeat this evil, terrifying regime".

- Lula urges caution -

Italy's Foreign Minister Antonio Tajani said Navalnaya's words "will make us feel the threat that weighs on Russian citizens and on every region of our Europe", where "violence, brutality, and war have been shamefully and irresponsibly returned".

But Lula's comments marked a sharp contrast to the messages coming out of many Western capitals, whose leaders have directly or indirectly blamed Putin for Navalny's death.

Speaking to reporters in Addis Ababa, where he was attending an African Union summit, Lula said it was important to avoid "speculation" and await the results of an autopsy.

"If you judge now and say I-don't-know-who ordered the killing and it wasn't them, afterwards you have to apologise. Why the rush to accuse?"

Navalny could have been sick or had a health problem, said Lula, warning against "trivialising" accusations of murder.

Lula has faced criticism in the West as overly soft on Putin, his fellow leader in the BRICS group -- which stands for Brazil, Russia, India, China and South Africa but recently expanded to include several other emerging powers.

Lula, 78, has been critical of the US and European responses to Russia's invasion of Ukraine, saying Kyiv shares the blame for the conflict and refusing to join Western sanctions on Moscow.

Kremlin spokesman Dmitry Peskov accused Western leaders on Friday of "absolutely unacceptable" and "hysterical" reactions to Navalny's death.

- Tributes continue -

The US ambassador to Moscow visited a makeshift shrine to Navalny on Sunday, as Russian authorities suppressed memorials and tributes to him.

Lynne Tracy was pictured at the Solovetsky Stone, a monument to political repression that has become a major site of tributes for Navalny.

At a separate makeshift memorial known as the "Wall of Grief", a bronze monument to Soviet-era repression, police had set up fences in a bid to ward off mourners.

Several dozen police officers could be seen standing nearby, but some people were allowed to enter through the fence and lay flowers, an AFP reporter saw.

Rights groups say police have detained more than 400 people at gatherings paying tribute to the opposition figure.

In several cities around Europe, Navalny supporters continued to pay tribute to him Sunday.

In Germany, people laid flowers and candles at a memorial in front of the Russian embassy in Berlin.

In Romania, a similar tribute appeared outside the Russian embassy in Bucharest.