ATHENS (Reuters) - The third migrant to perish in a week was found dead in his tent on Monday on Greece’s Lesbos island, raising alarm about the grim winter conditions in overcrowded camps that critics have denounced as deplorable.

FILE PHOTO - Refugees and migrants line up for food distribution at the Moria migrant camp on the island of Lesbos, Greece October 6, 2016. REUTERS/Alkis Konstantinidis/File Photo

The dead man is believed to be about 20 and from Pakistan, a police official on the island said. Another migrant who shared his tent was critically ill and taken to hospital.

The death at the island’s Moria camp follows those of a 22-year-old Egyptian and a 46-year-old Syrian who shared a tent and died days apart. Greek media reported they had inhaled fumes from a heater, but authorities would not confirm or deny that.

Greece’s migration minister Yannis Mouzalas ordered an investigation into the deaths, the causes of which remain unclear. Steps would be taken “to make the situation more manageable,” he was quoted by the Athens News Agency as saying.

“We wonder how many deaths it will take for the government to wake up,” said Stavros Theodorakis, leader of the small centrist party To Potami.

At least 3,000 refugees and migrants are living in Moria, a hilltop former military base where conditions have deteriorated as they await for months for word on their future.

The United Nations refugee agency and other international organizations have urged Greece to improve conditions at its overcrowded facilities.

“Something has got to give. We cannot tolerate this wanton loss of life,” said International Rescue Committee Greece director Panos Navrozidis, acknowledging that conditions in Moria did not meet humanitarian standards.

As a mid-winter freeze gripped parts of the country earlier this month, thousands of asylum-seekers endured sub-zero temperatures. Summer tents on Lesbos were weighed down by snow.

Across Greece, more than 60,000 refugees and migrants, most from Syria, Iraq and Afghanistan, have been stranded since last March in formal or makeshift camps which U.S.-based group Human Rights Watch has described as “deplorable and volatile.”

“We don’t know yet how they died but we do know the thousands stuck on the Greek islands have been suffering horrendous conditions in the cold, trapped by the failure of the EU to offer protection and dignity,” said Gauri van Gulik, Amnesty International’s Europe director.