Gaza’s militant Hamas rulers imposed a territory-wide curfew on Tuesday after authorities detected the first local cases of the coronavirus, raising fears of a wider outbreak in the blockaded territory that is home to some 2 million Palestinians.

Gaza has registered more than 100 cases and a fatality since the start of the pandemic, but until now all the infections were linked to quarantine facilities for returning travelers. Most lockdown restrictions were lifted months ago, with even wedding halls operating normally.

The four cases detected in central Gaza indicate the coronavirus has breached the territory’s defenses, and a wider outbreak could overwhelm a health care system battered by years of war and isolation, with only a few dozen ventilators for the entire population.

Gaza has also seen rising tensions in recent weeks between Israel and Hamas, as militants have launched incendiary balloons and rockets into Israel while demanding the easing of the blockade imposed when Hamas seized power in 2007. Israel has responded by tightening restrictions further and launching airstrikes against militant targets.

Hamas announced a 48-hour curfew after the four cases were announced late Monday. Schools, businesses, markets and mosques were ordered to close, and police patrols stopped and inspected the few cars passing through checkpoints.

The four patients are related and live in the al-Maghazi refugee camp in central Gaza. On Tuesday, Hamas-run police roamed the empty streets to enforce the lockdown.

Hundreds of people nevertheless took part in the funeral of four militants from the Islamic Jihad group who were killed in a mysterious blast late Monday in Gaza City.

The mourners, few of whom wore masks, marched shoulder to shoulder through the city’s crowded Shajaiyeh neighborhood despite calls from the group to take precautions and limit attendance to relatives of the slain militants.

All Gazans returning home through Israel or Egypt have been required to remain isolated at designated centers for 21 days. Authorities have detected 110 cases in the quarantine facilities since March, and 72 of them have recovered. A woman with underlying health problems died from the Covid-19 disease caused by the virus.

Abdelnasser Soboh, director of the World Health Organization’s Gaza office, said cases of local transmission were expected. “This was not surprising to us,” he said.

He added that authorities are following the correct procedures to track the source of the infection and people who were in contact with the patients.

The health ministry said a woman from Gaza who was allowed to travel to Jerusalem for medical treatment had tested positive after arriving there. Health workers back in Gaza then tested her family members, revealing the four cases. The woman is still in Jerusalem.

Hamas seized control of Gaza from rival Palestinian forces 13 years ago. In response, Egypt and Israel imposed a crippling blockade on the territory. Israel says the blockade is needed to keep Hamas from importing and manufacturing arms. Hamas and Israel have fought three wars and countless skirmishes.

There have been no deaths or serious injuries from the recent exchanges of fire, and neither side is believed to be seeking war. But any fatalities could spark an escalation.

The attacks were coordinated by Hamas to pressure Israel to ease the blockade. Instead, Israel has closed Gaza’s sole commercial crossing and its fishing zone. The territory’s only power plant was forced to shut down a week ago for lack of fuel, leaving most Gazans with just four hours of electricity per day.

Gaza’s heath infrastructure has been hollowed out by years of conflict, and would be ill-equipped to cope with a major outbreak. Gaza’s health facilities only have around 100 ventilators, more than half of which are already being used.

The U.N. agency for Palestinian refugees said it is “extremely concerned” by the closure of the power plant and its impact on Gaza residents.

“We are calling on all concerned parties to maintain a supply of electricity that is sufficient to meet the basic needs of the civilian population,” said Matthias Schmale, director of UNRWA affairs in Gaza.

Soboh of the WHO said that his organization managed to bring in 10 new ventilators for a special field hospital for coronavirus patients in Gaza, raising the number of these machines at that hospital to 50.

“We can deal with hundreds of patients, but not thousands,” he said.