After a period when coronavirus infections stayed very low in Israel, on Tuesday more than 100 new infections were reported over 24 hours for the first time in about two months.
Some 125 people had tested positive, the Health Ministry said.
The director-general of the Health Ministry, Chezy Levy, told Israeli television that about 70 per cent of the new infections were with the Delta variant.
Half of those infected were children, he said, and a third of those infected had been vaccinated.
The Delta variant was first discovered in India and is considered particularly contagious.
As recently as mid-June, new daily infections in Israel were only registering in the single digits. A requirement to wear masks was lifted nationwide last week.
Recent days have seen restrictions reimposed however. On Sunday pupils in two towns were again required to wear masks after an outbreak in schools.
The government also decided to expand the testing capacity for travellers at the airport.
Due to the rising numbers of infections and the spread of the Delta variant, the authorities are recommending the vaccination of 12- to 15-year-olds.
Previously, this had only been the case for high-risk patients and when travelling abroad.
Israel began its vaccination campaign early and 5.5 million people have already received a first vaccination and more than 5.1 million have also had a second jab.