Thousands of people gathered in central Moscow on Sundayto protest against their country's involvement in the conflict in eastern Ukraine at an All-Russian March for Peace, the first large anti-Kremlin rally since the conflict started in April.

The march for an "end to the Russian regime's irresponsible, aggressive policy" in Ukraine drew 5,000 protesters, according to the interior ministry. But official estimates of opposition march numbers have been notably low in the past, and the volunteer group White Counter, which was tallying participants as they passed through police metal detectors at the beginning of the march, said put the number at 26,000 people.

Although some far-left groups, such as Autonomous Action – whose members carried a banner reading "No to war between peoples! No to peace between classes!" – participated in the march, the main contingent of the protest was similar to the movement that shook Moscow in 2011-2013. Other banners read "Hands off of Ukraine!" and "Freedom to the 6 May prisoners", a reference to those jailed on charges of inciting riots after an anti-Putin rally in Bolotnaya Square on 6 May 2012 that degenerated into clashes between police and protesters.

Others carried pictures of Russian soldiers killed in Ukraine. In recent weeks, Russian independent media have reported on the growing number of soldiers who have gone missing after being deployed to eastern Ukraine, and secretive funerals have been held for some servicemen in places like the provincial city of Pskov.

Sunday's march was organised by longstanding opposition parties including Yabloko, Solidarity and Parnas, as well as newcomers like the Party of Progress organised by popular anti-corruption campaigner Alexei Navalny, who is currently under house arrest as part of what many see as a politically motivated criminal case.

The protesters represented a variety of political views, but most were united in their opposition to what they see as a Kremlin policy to escalate the conflict in eastern Ukraine by sending arms and soldiers across the border.

"My last name may be the same as Putin's, but I'm against him," said Oksana Putina. "We can wake up the Russian people, so that we won't see any more Russian troops in Ukraine … Let Putin take out his troops, and Ukraine will deal with its own problems."

Vadim Kryuchkov and Varvara Daryevskaya, who were holding Russian and Ukrainian flags, said they didn't believe the protest would change the Kremlin's course but felt it was their duty to express their opposition. Kryuchkov said he was originally from a town near Luhansk and supported the greater local autonomy for the region, but was against Russia sending troops and arms to eastern Ukraine. "We want Ukraine to see that there are people in Russia who don't support the war," Kryuchkov said. "Russia is directly participating in this war."

"In fact, Russia started it," Daryevskaya said.

A few thousand protesters also assembled in St Petersburg, while peace marches in other cities drew far fewer people. According to the human rights organisation OVD Info, a peace march organiser in Yekaterinburg was briefly detained by police but later returned to the protest.

The Moscow march was tailed by a few hundred pro-Kremlin protesters holding the flags of the Donetsk and Luhansk people's republics declared by pro-Russian rebels in eastern Ukraine. At least one minor scuffle broke out but lines of riot police for the most part kept the two camps apart.

"The whole reason for this crisis is that Russia has refused to recognise Ukraine's European choice," said Higher School of Economics professor Nina Belyayeva, who was holding a sign reading, "Ukraine's European choice = an example for Russia". She was soon confronted by several pro-Kremlin protesters, who argued that the protests in Kiev this winter that toppled former Ukrainian president Viktor Yanukovich's regime had been organised by the United States.

Police did confiscate signs from some protesters, including one reading, "Putler kaput!" When asked about the seizure, a police officer would only say that the signs "didn't correspond to the topic of the protest".

"It strongly affects the police officers' nerves when it's something related to Putin," said organiser Ilya Mishenko.