A Saudi Arabia-led coalition carried out strikes on targets in Yemen after intercepting and destroying a drone that attempted to attack Abha International Airport, the kingdom's state media reported on Thursday. The coalition was taking “operational measures to deal with the sources of hostile cross-border attacks”, Saudi Arabian news agency SPA reported. The strikes were aimed at workshops and warehouses for ballistic missiles, drones and communications systems in the provinces of Sanaa, Dhamar, Saada and al-Jawf in response to ballistic and drone threats, state TV reported. The coalition said it targeted what was described as a secret plant for experts from the Islamic Revolutionary Guard Corps and Lebanon's Hezbollah, which it accuses of being involved in hostile attacks against the kingdom. Earlier, the coalition intercepted and destroyed a drone that attempted to attack Saudi Arabia's Abha International Airport in Asir province, SPA said. The coalition said it was taking “operational measures to deal with the sources of hostile cross-border attacks”, the state news agency reported. The military coalition led by Saudi Arabia intervened in Yemen in March 2015 after the Iran-backed Houthi group ousted the government from the capital Sanaa. On Wednesday, the UN called for the immediate release of two of its employees detained by Houthi rebels in Sanaa. The employees of Yemeni nationality were held with no explanation and in breach of their international immunity, UN spokesman Stephane Dujarric said. “The Secretary General is deeply concerned about the arrests and detention of two UN staff members in Sanaa by the Houthis earlier this month,” he said. Since the arrests on November 5 and 7 in the rebel-held capital, it has been impossible for their families and offices to communicate with them, Mr Dujarric said. One works for Unesco and the other for the UN human rights department. Last week the Houthi militants said they were holding them and gave assurances that the two would be released but they remain in detention “in breach of UN privileges and immunities”, the spokesman said. Also, the US had called on the militant group to release Yemenis who work for the US embassy after the diplomatic compound was breached by Houthis. The US shifted embassy operations to Saudi Arabia in 2015 because of the war in Yemen. Mr Dujarric declined to say if the two cases were related. The seven-year war has created what the UN has described as the world's worst humanitarian crisis. About 80 per cent of Yemen's 30 million people rely on aid to survive. Tens of thousands of people, mostly civilians, have died in the fighting and millions have been forced from their homes.