Moscow (CNN) -- Four people face criminal charges in connection with the sinking of a Russian ship Sunday in which scores of people died, federal investigators said Tuesday.

Both Svetlana Inyakina, general director of Argorechtur, the company that rented the cruise boat "Bulgaria," and Yakov Ivashov, a manager at the Kama River Register, have been detained, Russia's Investigative Committee said.

They are charged with providing services that do not meet safety standards which resulted in multiple deaths, and if convicted could be jailed for up to 10 years.

Criminal charges are also being brought against the captains of two ships which are accused of passing the sinking boat without stopping to help the people in the water, the committee said. They could face heavy fines or up to three years in prison.

At least 116 people died in the accident, the committee said on its website. The Russian Emergency Situations Ministry said it has recovered 90 bodies so far -- of 60 women, 16 children and 14 men.

Russian Transport Minister Igor Levitin, who is also head of the special government commission investigating the accident, said 22 people were buried Tuesday, and more are expected in the coming days.

Divers will search around the clock until all of the victims are found, said Levitin. Recovery efforts will also include small planes conducting reconnaissance flights as far as 80 miles downstream, the minister said.

According to Russian state TV, scuba divers are working underwater in low visibility and against a heavy current that is moving the boat, which is lying at the bottom of the river.

Earlier Tuesday, divers broke through to an inner room where a children's karaoke concert was taking place when the boat capsized, emergency officials said.

Officials believe dozens of children were trapped in the recreation room Sunday when the "Bulgaria" sank on the Volga river in the Russian republic of Tatarstan with about 200 people on board.

There are 175 scuba divers working on the scene, the ministry said.

Russia is observing a day of mourning Tuesday with church services taking place all across the country, flags flying at half-staff and national television canceling all entertainment programming in the wake of what Russian media are calling the most devastating river accident in the country's history.

Prime Minister Vladimir Putin said the federal government would pay 1 million rubles ($35,500) to the families of each of the dead. He also promised 400,000 rubles ($14,250) to those who suffered major and moderately severe injuries, and half that sum to people with minor injuries.

Among the bodies to have been recovered are those of the ship's captain Alexander Ostrovsky and his wife, local officials in Tatarstan told Russian media at the site of the accident.

Russian Emergency Situations Minister Sergei Shoigu said the lifting of the boat will start late afternoon Saturday.

At least 79 people have been rescued, some of whom have been released from hospitals after receiving medical treatment, according to government agencies.

The ship did not have a license to transport passengers, was overloaded, and was last repaired more than 30 years ago, the Russian Prosecutor's Office said Monday.

Prosecutors also established that the left engine of the ship was damaged, they said on their website.

Russian state TV reported the vessel had an operational limit of about 150 passengers, citing a top government official on site. State TV also reported, citing law enforcement officials, that there were life vests on board for only 156 people.

The Investigative Committee said Tuesday there were 192 people aboard the boat -- 148 passengers, plus 44 staff and their relatives.

Shoigu said earlier there were 208 people aboard the ship, of whom 25 passengers were not officially registered and didn't have tickets. RIA Novosti reported that 205 people were on board.

Russian President Dmitry Medvedev said it was evident from the information gathered so far "that the vessel was not in the appropriate condition."

"We have to establish why the owner of the ship operated a ship that was in such a poor technical condition," Medvedev said. "It is clear that such an accident couldn't have taken place if safety rules were followed, even despite the difficult weather situation."

He also called for "a total inspection of all public carriers in Russia," adding that it is "obvious that this ship was not the only one with issues.

"The number of old tubs that are now in use (in Russia) is just staggering," the president said.

He instructed the Prosecutor General's Office to investigate everyone involved in the Bulgaria cruise, including "ship-owners, those who issued the navigation permit and those who were involved in organizing that boat tour, especially given the large number of children aboard."

Authorities have not ruled out the possibility that some passengers could have survived by swimming to the bank or one of the islands in the Volga.

Survivors told Russian state TV that there were many children on board the ship.

The ferry was built in 1955 in what used to be Czechoslovakia, according to Russian law enforcement officials.

RIA Novosti said the double-deck cruise ship went down near the village of Syukeyevo in Tatarstan, about 80 kilometers (50 miles) south of the city of Kazan. Kazan is about 724 kilometers (450 miles) east of Moscow.

CNN's Arkady Irshenko contributed to this report.