A new flight has been chartered by the UK government for British nationals to leave Lebanon on Sunday, amid the growing conflict in the region.

More than 250 UK citizens have left Lebanon on government-chartered flights amid the conflict, the Foreign Office said. The UK chartered a fourth flight to leave Beirut-Rafic Hariri airport in Beirut on Sunday.

The government said there were no further flights scheduled owing to “significantly reduced” demand, though it said it would keep the situation under constant review.

The Foreign Office said extra capacity had been arranged “due to high demand for places on commercial flights, and has enabled more than 250 additional people to leave in the last week … However, demand has now significantly reduced and this Sunday’s flight is currently the only one scheduled.”

British nationals and their spouses or partners, and children under the age of 18, are eligible to book a place on Sunday. All passengers must hold a valid travel document and dependants who are not UK citizens will require a valid visa that has been granted for a period of stay in Britain of more than six months.

The foreign secretary, David Lammy, said: “The situation in Lebanon remains volatile, so I am glad that we have helped the many people who have heeded our advice to leave the country immediately. With demand falling, and the security situation deteriorating, there is no guarantee other options to leave quickly will become available. I urge anyone who wants to leave to register now.”

The government has announced a further £10m aid package for Beirut in response to concerns over a lack of shelter and reduced access to clean water, hygiene and healthcare. It is also continuing efforts to help Britons leave Lebanon by trying to increase capacity on commercial flights. About 700 troops and Foreign Office and Home Office staff, including Border Force officers, have been deployed to Cyprus in case an emergency evacuation is needed.

Keir Starmer urged British nationals still in the country to come forward to be evacuated. Speaking to reporters during a visit to Cheshire on Friday, the prime minister said: “To everybody listening who may be in that position: now is the time to leave, we have got the plans in place. So please come forward and we can make sure that they are evacuated.”

Israel launched a ground incursion into Lebanon on Monday and its forces have been clashing with Hezbollah militants in a narrow strip along the border. Before the incursion, strikes in Lebanon by Israel killed the long-time Hezbollah leader Hassan Nasrallah and many other top commanders.