MOSCOW — Thousands of Russians gathered Tuesday in front of the main municipal building in the Siberian city of Kemerovo to demand answers following Sunday’s fire in a local mall, which killed at least 64 people — 41 of them reported to be children.

The disaster at the Winter Cherry mall has gripped the nation. The fire’s cause has not yet been determined, but local officials say a child may have lit a foam ball in a play area. The blaze quickly engulfed the mall’s top floor, trapping children in a nearby movie theater.

Fire alarms did not sound, and fire doors were locked. An investigative committee said that the alarms have been out of service since March 19 and that a security guard neglected to trip manual alarms once the blaze was reported.

President Vladimir Putin flew to the city, about 2,000 miles east of Moscow, to meet with local officials and calm speculation that many more people died than officially reported.

At first, about a dozen demonstrators gathered Tuesday morning to call for a full probe of the fire. Their ranks grew throughout the day to an estimated 4,000, according to video footage from the scene. Many of the demonstrators doubt the official count of 64 dead, alleging that the toll is much higher.

“Truth! Truth!” they chanted. “How many dead?”

They also called for the resignation of Kemerovo Mayor Ilya Seredyuk and the regional governor, Aman Tuleyev. Footage showed riot police in tactical gear standing between people and the administration building.

“Resign! Take them to court!” the demonstrators shouted.

Authorities reportedly have detained four people for questioning in the case, including the director of a company that rents the mall’s top two floors.

Sunday’s fire apparently claimed an entire class of schoolchildren, some of whom died after calling parents or other relatives on their cellphones to say goodbye. Others posted desperate messages on social media before falling silent.

During Putin’s meeting with local officials, Tuleyev apologized to him for what happened in Kemerovo but not to the demonstrators outside.

Instead, according to Russian broadcaster RBC, Tuleyev told Putin that the demonstration was attended by just 200 of the usual suspects — opposition protesters, rather than the families of the dead and their outraged compatriots.

Meanwhile, Deputy Governor Sergey Tsivilev took a different tack. Later in the day, he came out and begged the crowd for forgiveness on bended knee.

Seredyuk, the mayor, also ventured out to invite a group of 15 demonstrators to visit the morgue with him to see the bodies.

According to the Interfax news agency, one of the group’s members confirmed the official count of 64 dead.

“We have inspected the morgue,” the demonstrator, who was not named in the report, was quoted as saying. “We have seen the bodies. Judging by their size, there are some 20 adults in the morgue. The others are children. The bodies have not been hidden.”

Interfax said semiofficial lists of the victims include the names of 41 children.

Putin urged people to wait for the full investigation before assigning blame, assuring them that officials found responsible would be punished, regardless of their rank or standing.

“People, children came there to have a good time,” he told ministers in a meeting, according to Interfax. “Why? It is because of criminal negligence and disorderliness.”

Demonstrators also expressed frustration over the lack of official events mourning the dead. Later in the day, Putin signed an order declaring Wednesday a national day of mourning, the Kremlin said.

In Moscow, two separate memorial vigils were staged Tuesday evening at opposite ends of the city center.

After opposition leader Dmitry Gudkov called for Muscovites to gather at Pushkin Square at 7 p.m. to lay flowers and mourn the dead, the Moscow mayor’s office announced a meeting next to the Kremlin at 5 p.m.

Both vigils were solemn, although the later one was much larger — drawing a few thousand people.

Despite attendance by opposition figures including Alexei Navalny, Gudkov stressed that it was not an opposition protest. The gathering was technically unsanctioned by authorities, but police made no effort to disperse the crowd. People stood mostly in silence with black signs and balloons.

Some people attended both meetings. One participant at the Pushkin Square event, identified only as Maria, told the RBC news service that as many vigils should be held as possible.

A vigil was also organized in St. Petersburg.

As part of apparent efforts to regain control of the narrative, Foreign Ministry spokeswoman Maria Zakharova said that coordinated U.S. and European expulsions of Russian diplomats Monday showed disrespect for the dead. The Russians were ordered expelled in retaliation for the poisoning of a former Russian spy and his daughter in Britain this month, a nerve-agent attack attributed to Moscow.

“We have learned a lot about the politicians of Europe and America today,” she said. “We have always sympathized with the Americans and the Europeans during their moments of grief. . . . This is hard to believe and to forget.”

In Washington on Monday, Russian Ambassador Anatoly Antonov was more explicit.

“Today . . . we have seen that Washington is emotionally deaf, indifferent and heartless,” he said. “Ordinary Americans sympathized with our grief and send their condolences.”

“Thank you, friends,” he said.

U.S. Ambassador to Russia Jon M. Huntsman Jr. was asked by Kommersant newspaper about the decision to expel the diplomats on the day after the fire, and he said that there were simply too many countries involved to delay the action.