A lockdown began in Gaza on Tuesday after the first cases of Covid-19 were confirmed among the general population in the Palestinian enclave, whose restricted borders have spared it from widespread infection. Health authorities in the Hamas-run territory of two million people are concerned over the potentially disastrous combination of poverty, densely populated refugee camps and limited hospital facilities. Until now, all cases reported in Gaza were linked to quarantine centres for residents returning from abroad. The Health Ministry said four people from the same family have tested positive for the virus in central Gaza and investigations were under way to track the source of the infection. A full lockdown was imposed on Al Maghazi refugee camp, where the family lives. The ministry said a woman from Gaza who was allowed to travel to Jerusalem for medical treatment tested positive. Health workers in Gaza then tested her family members, revealing the other three cases. Hamas announced a 48-hour curfew in the entire territory, closing businesses, schools, mosques and cafes. Hamas seized control from rival Palestinian forces of Fatah, which rules the West Bank, in 2007. In response, Egypt and Israel imposed a crippling blockade on the territory. Israel says the blockade is needed to keep Hamas from importing and making weapons. Hamas and Israel have fought three wars and smaller clashes in the past 13 years. Israeli tanks and aircraft carried out strikes on Hamas targets in Gaza overnight in response to the launch of balloons carrying incendiary material across the border, the army said on Tuesday. Israel has bombed the Hamas-ruled enclave almost daily since August 6, in response to the balloons and, less frequently, rockets launched across the border. The flare-up came after US Secretary of State Mike Pompeo visited Israel on Monday and as British Foreign Secretary Dominic Raab was due to hold talks in Israel and the Palestinian Territories on Tuesday. The fire balloons – makeshift incendiary devices fitted to inflated balloons or plastic bags – have sparked several blazes on farmland in southern Israel, causing significant damage to crops. They are widely seen as an attempt by Hamas to improve the terms of an informal truce from 2014 under which Israel committed to ease its blockade in return for calm on the border. But so far, Israel's response has been to tighten the blockade. It has banned Gaza fishermen from going to sea and closed its goods crossing with the territory, prompting the closure of Gaza's sole power plant for want of fuel.