The Israeli health ministry reimposed a requirement Friday for masks to be worn in enclosed public places, following a surge in Covid-19 cases since the rule was dropped 10 days ago.
The spike in new infections is a blow for a country which has prided itself on one of the world's most rapid and comprehensive vaccine rollouts.
The head of Israel's pandemic response taskforce, Nachman Ash, told public radio the requirement came after four straight days of more than 100 new cases per day, with 227 cases confirmed Thursday.
"We are seeing a doubling every few days," Ash said.
"Another thing that's worrying is that the infections are spreading. If we had two cities where most of the infections were, we have more cities where the numbers are rising and communities where the cases are going up."
Ash said the rise in cases was likely due to the highly contagious Delta variant of the virus, first identified in India.
Reimposing the mask requirement is a setback for Israel, just days after it was lifted on June 15.
Some 5.2 million people in the country have received both doses of the Pfizer-BioNTech vaccine.
Ash said despite the increased number of positive cases, he did not yet see a parallel rise in hospitalisations or deaths.
"It's clear it's a factor of time, that not enough time has passed," Ash said. "But we hope the vaccines will protect us from a rise in hospitalisation and difficult cases."
- Pride march with few masks -
The health ministry urged Israelis to wear masks in crowded outdoor spaces too.
But a pride march Friday afternoon in Tel Aviv saw tens of thousands of people dancing in the streets, many without masks, according to an AFP reporter.
The event, which organisers called the largest of its kind worldwide since the start of the pandemic, had been suspended last year due to the virus.
The return of masks met a mixed reception.
Hadar Lavy, in Jerusalem, said she was not pleased, saying that "our smiles are much more important than masks."
But Esther Hamshalom, another Jerusalem resident, said it was better to be safe than sorry.
"The mask all the time, inside, outside," she said. "I feel safety with the mask, so it's better for us."
Israel became a pioneer in Covid inoculations after then prime minister Benjamin Netanyahu obtained millions of doses from Pfizer in exchange for sharing health data on their impact.
The resulting fall in new cases allowed a broad return to normality -- but it did not save Netanyahu's job.
He was replaced as prime minister earlier this month by his former aide turned foe Naftali Bennett.
Bennett warned Tuesday of a "new outbreak" of coronavirus, asking Israelis to cancel their travel plans and delaying plans to reopen the country's borders to individual tourists.
Bennett urged parents to vaccinate children aged 12 and older "as soon as possible," noting that Israel's stock of vaccines would soon expire.
A deal to trade soon-to-expire vaccines with the Palestinian Authority for new shots arriving in the autumn fell apart last week amid mutual accusations of bad faith.
Israel has faced criticism for refusing to vaccinate most Palestinians living in the West Bank, or in the Gaza Strip, which is under Israeli blockade.