Spanish soldiers - deployed to help battle the new virus outbreak - have found elderly patients abandoned in retirement homes, and sometimes even dead in their beds, Spanish Defence Minister Margarita Robles has said.
The defence ministry said that staff at some care homes had left after the coronavirus was detected, BBC reported.
"The government was going to be strict and inflexible when dealing with the way older people are treated" in retirement homes," the minister added.
Spanish prosecutors said an investigation had been launched.
The military has been brought in to help disinfect care homes in Spain, one of Europe's worst hit countries.
Meanwhile, an ice rink in Madrid is to be used as a temporary mortuary for Covid-19 victims, officials said.
On March 23, Spain recorded its highest daily death toll - 462 - bringing the total to 2,182.
Health officials have said that in normal circumstances the bodies of deceased residents are put in cold storage until they are collected by the funeral services.
But when the cause of death is suspected to be linked to coronavirus they are left in their beds until they can be retrieved by properly equipped funeral staff. In the capital Madrid, which has seen the highest number of cases and deaths, that could take up to 24 hours, officials said.
Spanish Health Minister Salvador Illa told a news conference that retirement homes were "an absolute priority for the government".
"We will exercise the most intensive monitoring of these centres," she added.
As the crisis in Madrid worsened, the city's municipal funeral home said it would stop the collection of Covid-19 victims from Tuesday because of a lack of protective equipment.
The city is to use a major ice rink, the Palacio de Hielo (Ice Palace), as a temporary mortuary where bodies will be stored until funeral homes can collect them, officials told Spanish media.
The Palacio de Hielo complex, which also includes shops, restaurants, a bowling alley and cinemas, is not far from the Ifema congress centre where a field hospital has been set up for coronavirus patients.
Spain is the second worst affected country in Europe after Italy, which now has the highest number of coronavirus-related deaths in the world.
Italian authorities said on Monday that 602 people with Covid-19 had died in the past 24 hours, bringing the total to 6,077.
But the daily increase was the smallest since Thursday, raising hope that stringent restrictions imposed by the government were starting to have an effect.