The deadly exchange of fire between Palestinian militants in the Gaza Strip and the Israeli military has escalated significantly, with the UN fearing a "full-scale war". More than 1,000 rockets have now been fired by Palestinian militants over 38 hours, Israel said, most at Tel Aviv. Israel has carried out deadly air strikes, bringing down two tower blocks in Gaza on Tuesday. At least 43 Palestinians and six Israelis have been killed since Monday. That includes 13 Arab Israeli children caught up in the conflict. UN Secretary-General António Guterres said he was "gravely concerned" by the ongoing violence. The latest fatality was an Israeli citizen, who was killed when an anti-tank guided missile, fired from the northern Gaza Strip, struck a jeep on the border. Three other people were injured. Israeli Arabs have also staged violent protests in a number of Israeli towns. The city of Lod, near Tel Aviv, has been put under a state of emergency. A 52-year-old father and his 16-year-old daughter reportedly died in Lod when a rocket hit their car, Israeli media are reporting. In Gaza, the streets are full of rubble where buildings have collapsed and cars are crushed or burned from Israeli air strikes. The fighting follows weeks of rising tension stoked by violent confrontations between Israeli police and Palestinian protesters at a site in Jerusalem that is holy to both Muslims and Jews. Israel's military says this is the biggest exchange since 2014. Of the 1,050 rockets and mortar shells that have now been fired from Gaza, 850 had landed in Israel or were intercepted by its Iron Dome air defence system, and 200 failed to clear the border and landed back in Gaza, the Israeli army said. Video footage from the city showed rockets streaking through the night sky, some exploding as they were hit by Israeli interceptor missiles. Loud booms and air-raid sirens were heard across targeted cities, which included Tel Aviv, Ashkelon, Modiin, and the southern city of Beersheba, as Palestinian militants tried to overwhelm missile defences. Anna Ahronheim, the defence and security correspondent of the Jerusalem Post, told the BBC: "To hear hundreds of interceptions and even to hear rockets fall near us was horrifying." The rocket fire escalated after the two residential tower blocks were brought down in Gaza. Israel said it was targeting rocket launch sites, high-rise buildings, homes and offices used by Hamas, the militant group that rules Gaza. Hamas said it was incensed by the "the enemy's targeting of residential towers". Residents had been warned to evacuate the buildings before the fighter jets attacked, however health officials said there were still civilians deaths.