ATHENS (Reuters) - Hundreds of asylum seekers protested conditions at Greece’s biggest migrant camp on Lesbos on Tuesday after a woman was killed in a fire there, marching towards the island’s capital before being halted by police.

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More than 12,000 people - mainly from Syria, Afghanistan and Iraq - live in Moria camp, which has grown to become the island’s second largest town in just three years.

The woman’s death on Sunday was the third there in two months. An Afghan teenager was killed in a fight in August and a five-year-old Afghan boy was accidentally run over by a truck while playing in a cardboard box outside the camp in September.

Holding signs reading “Moria is hell” and “We want security and freedom”, the protesters were prevented from marching farther than a few hundred meters (yards) from the camp’s gates by around two dozen riot police.

Moria, in a former military base, opened in 2015 as a center to register new arrivals but is now at four times its capacity and it has spilled over into a muddy, garbage-strewn olive grove.

Since the European Union struck a deal with Ankara in 2016 to cut off refugee and migrant flows to Greece from Turkey, asylum seekers have been barred from leaving any of the Greek island camps set up to process them until their claims are assessed.

In Moria, several people share flimsy tents packed next to one another. Women have told humanitarian organizations they feel unsafe at night and sanitary conditions have been described by aid groups “horrendous,” with over 100 people sharing one toilet.

Four other island camps near Turkey are also holding thousands of people.

“Keeping people on the islands in these inadequate and insecure conditions is inhumane and must come to an end,” said a spokeswoman for United Nations refugee agency UNHCR in Geneva.

More than 10,000 people, mostly Afghan and Syrian families, crossed the Aegean Sea from Turkey to Greece in September according to UNHCR, the highest monthly level in over three years.

On Monday, Greece’s government outlined a shift in migration policy, saying it would tighten its sea and land borders, shorten the asylum process and deport 10,000 people who do not qualify for protection by the end of next year.

Migration Minister Giorgos Koumoutsakos said Greece was currently handling about 75,000 asylum claims.