Detentions ordered after Russian riverboat sinking

* Survivors said two vessels passed site of sinking

* Death toll in Volga River disaster at 114

By Steve Gutterman

MOSCOW, July 15 (Reuters) - Russian investigators ordered police on Friday to detain the captains of two vessels that survivors from a sunken riverboat said passed them in the water without stopping to help.

The two captains will be held for questioning, federal Investigative Committee spokesman Vladimir Markin said.

Survivors who escaped when a tourist boat with 208 people on board sank in the Volga River on Sunday said they watched two commercial vessels pass by as they struggled to stay afloat.

One man said he and other survivors waved their arms repeatedly to no avail, and Russian media reported that people on the passing craft snapped cell-phone photos as they went by.

The confirmed death toll in Russia's worst river disaster in nearly three decades reached 114 on Friday as emergency officials said divers had searched all accessible parts of the riverboat Bulgaria, which sank swiftly to the bottom.

Another 15 people were still missing and feared dead, while 79 survived -- all but a few of them rescued by another tourist boat that came along more than an hour after the Bulgaria sank 3 km (1.85 miles) from shore in a rainstorm.

The sinking of the overcrowded, 56-year-old boat rekindled concerns about the negligence and corruption that leads to deadly accidents in Russia and the condition of boats, planes, factories and facilities built in the Soviet era.

Prime Minister Vladimir Putin, whose record in a decade in power has been marred by such disasters, visited the Volga on Thursday evening and said the lives lost in the river were the price Russia pays for "irresponsibility, complacency and greed".

Putin, president from 2000-2008, has hinted he will return to the country's top office in a March 2012 election or endorse President Dmitry Medvedev for a new term.

Both have talked tough and called for stricter safety controls after deadly accidents and militant attacks, but critics say they have been unable to make significant progress in curbing corruption and negligence.

Authorities have arrested the head of the tour company that leased the Bulgaria, as well as a river transport inspector. (Editing by Jon Hemming)