The Lebanese militant group Hezbollah has vowed to retaliate for Israeli airstrikes on southern Lebanon that killed three of its fighters and 10 other people, including four children. A strike on the city of Nabatiyeh late on Wednesday killed seven civilians, including two children, and three members of Hezbollah, sources in Lebanon said. It followed an earlier attack that killed a woman and her two children in the village of Souaneh at the boundary between the two countries. Israel said that one of the dead fighters was a senior commander in Hezbollah’s elite Radwan force, as Israel’s defence minister, Yoav Gallant, warned Hezbollah that the Lebanese capital, Beirut, could be targeted in the event of an escalation into full-scale war. Speaking at the end of a training exercise on Thursday, Gallant said: “Hezbollah escalated by half a click – we escalated with a full step,” adding: “We could attack not just 20km inside [Lebanon], but 50km, and in Beirut, and anywhere else.” The Hezbollah politician Hassan Fadlallah said: “The enemy will pay the price for these crimes,. The resistance will continue to practise its legitimate right to defend its people.” Israel launched what it described as “intensive” strikes on southern Lebanon just hours after projectiles from Lebanon killed an Israeli soldier in Safed. More heavy Israeli strikes were reported in south Lebanon on Thursday after anti-tank missiles were fired into Israel earlier in the day, as Lebanon’s caretaker prime minister, Najib Mikati, condemned the latest escalation. “At a time where we are insisting on calm and call all sides to not escalate, we find the Israeli enemy extending its aggression,” a statement from his office said. The veteran Lebanese politician and speaker of the country’s parliament, Nabih Berri, also condemned what he called the “massacre” by Israel on Wednesday evening in Nabatiyeh. “The bloodshed in Nabatiyeh is in the hands of international envoys, the United Nations and human rights organisations, not so that they condemn what happened but so that they act urgently” to stop Israel, he said in a statement. Amid concern that the conflict in Lebanon had climbed another rung in intensity, the outgoing interior minister, Bassam Mawlawi, said he feared “the war was moving closer to the heart of Lebanese territory”. “We must remain committed to international law and international resolutions to avoid war,” he said in an interview in the immediate aftermath of the Israeli strikes. Underlining the sense of alarm over the latest developments, a spokesperson for the UN peacekeeping mission in Lebanon described a “concerning transformation” in the conflict. “Attacks targeting civilians are violations of international law and constitute war crimes,” Andrea Tenenti said in a statement. The strikes were the heaviest since cross-border exchanges began between militant groups in Lebanon and the Israel Defense Forces (IDF) on 8 October, the day after Hamas’s incursion in southern Israeli in which about 1,200 people were killed. The exchanges have become gradually more serious, displacing tens of thousands of people on both sides of the border. As the scope of the confrontation has spread ever wider, Israel has pursued a campaign of targeted assassinations, killing a senior Hamas official in a Beirut suburb and a number of senior Hezbollah commanders as diplomatic efforts, anchored by the US, continue in an attempt to bring an end to the fighting. Both sides have said they do not seek all-out war, and the conflict has largely been contained in areas near the boundary. A source familiar with Hezbollah’s thinking said the attack on Nabatiyeh marked an Israeli escalation but was still within unwritten “rules of engagement” between the two sides. The latest strikes, however, come as speculation increases in Israel about a wider conflict amid growing political frustration over the displacement of the population close to the border. The civilian deaths in Lebanon follow a series of deadly exchanges this week. On Tuesday, the IDF killed nine Hezbollah and Islamic Jihad fighters which, in turn, prompted a Hezbollah rocket barrage in the Safed region on Wednesday morning that killed an Israeli soldier and injured eight other people when one of the missiles landed in the IDF’s northern command headquarters. The IDF responded to that attack with a series large-scale airstrikes in Lebanon, including the strikes on Nabatiyeh and Souaneh. The strike on Nabatiyeh destroyed part of a building, killing seven members of the Berjawi family. Hussein Badir, a neighbour of the family, said he and other neighbours had rushed to the street to dig through the rubble. He said the family was “decent and respectable” and “not involved in anything”. For Badir, the strike brought back memories of Israel’s bombardments during its 2006 war with Hezbollah and also of a 1996 offensive. “Nobody is doing anything to help us,” he said. “It’s our right to defend ourselves in our country in Lebanon.” As clashes continued on Thursday, the IDF said it had hit a large number of sites in the region of the village of Wadi Slouki, close to the boundary town of Marjeyoun, that it said were used for firing missiles at Israel, as well as buildings and infrastructure. Government institutions, schools and the Lebanese University were to close on Thursday in protest against the airstrikes.