JERUSALEM – The start of the Jewish Day of Atonement at sundown Sunday marked the beginning of a day like no other in Israel, on which even Israelis with no connection to religion tend to put their normal lives on hold.

This year Yom Kippur, the holiest day of the Jewish calendar, comes at a particularly somber time following revelations of a previously hidden Iranian nuclear facility and more missile tests by the Revolutionary Guard.

"That proves to whoever was still in doubt that Iran is the most serious threat today on the peace of the world and its security," said Israeli Deputy Foreign Ministry Danny Ayalon, speaking to Israeli Channel 10.

Israel considers Iran a strategic threat due to its nuclear program, missile development and repeated references by Iranian President Mahmoud Ahmadinejad to Israel's destruction.

When Yom Kippur began at around 5 p.m. local time, TV and radio stations blinked off the air, flights in and out of Israel's international airport ceased, and nearly all businesses closed. The streets emptied of cars and cities and highways were eerily quiet.

The country's ordinary bustle receded to the cities and towns that are home to the one-fifth of Israelis who are Muslims and Christians.

But the holiday's apparent calm conflicted with many Israelis' fears about the perceived Iranian threat.

Israel has long said Iran is seeking nuclear weapons, while Tehran insists its facilities are only for producing fuel for power plants.

Many Israelis felt vindicated this week, however, when evidence of a clandestine facility was presented on Friday by President Barack Obama and the leaders of Britain and France at the G-20 economic summit in Pittsburgh.

The facility enriches uranium fuel to power nuclear reactors. Highly enriched fuel, however, can also be used to make weapons.

Israel is widely believed to have a nuclear arsenal of its own.

Even inside Israel, the run-up to the holiday was less than calm. Israeli police used stun grenades to disperse Palestinian rioters on Jerusalem's Temple Mount, known to Muslims as the Noble Sanctuary, police said.

The incident took place during a visit by a Jewish group to the site. Deadly violence has erupted there several times in the past.

Police spokesman Shmuel Ben-Ruby said around 150 Palestinians threw stones at the Jews visiting the site, which is open to non-Muslims at certain hours.

Police dispersed the rioters using stun grenades, and two policemen were lightly injured.

Rabah Bkirat, an official with the Muslim religious body in charge of managing the site, said some of the protesters had come because of rumors of an "invasion" by Jewish settlers. When a group of some 15 Jews entered the grounds accompanied by police, the protesters began chanting slogans and only threw stones after police used force, he said.

Eleven Palestinians sustained minor injuries in the clashes, Bkirat said.

Sunday's violence did not affect prayers at the Western Wall ahead of Yom Kippur, the holiest day on the Jewish calendar, which starts Sunday at sundown and ends sundown Monday.

According to tradition, Jews must spend Yom Kippur day fasting, praying and repenting for past sins in the hopes of receiving divine forgiveness before God seals their fate for the upcoming year.

Israel has a large population of religious Jews who observe all the Jewish festivals, but Yom Kippur is unique among Jewish holidays for its resonance among people who are distant from religion during the rest of the year. Most Israeli Jews say they fast, and almost no one dares drive a car. Many will not even talk on the phone, surf the Internet or turn on a television.

"For the average secular Israeli, this is a day to connect with his spirituality and his Judaism, even though he is not religious," said Rabbi David Stav, one of the founders of Tzohar, an organization dedicated to making Judaism more accessible to secular Israelis.

"He fasts, he prays, he doesn't work or watch television — the day is dedicated to matters of the spirit," Stav said.

In the days leading up to the fast, some Orthodox Jews perform a ceremony known as "kaparot," or "atonements," in which a person's sins are symbolically transferred to an animal, usually a chicken, which is then slaughtered and eaten.

Fainting, dehydration and other fasting-related complaints are common, and Israeli emergency services went on high alert.

While the day is largely solemn, it has its lighter side. The streets, emptied of cars, fill up with children on bicycles and skateboards taking advantage of the rare opportunity to ride down the middle of the road.

The Israeli military says the West Bank will be under closure until the holiday's end due to security concerns.

A military spokesman said the closure will be in effect from midnight Saturday until after the holiday.

Israel has imposed West Bank closures during most Jewish holidays in recent years due to concerns that Palestinian militants could take advantage of the festival to carry out attacks inside Israel.