Israeli leaders warned the army was prepared to meet all threats facing it, as they paid tribute to fallen troops and civilian deaths in terror attacks at Memorial Day ceremonies on Sunday.
"Since our inception as a people, we had to fight for our freedom and our existence," Prime Minister Benjamin Netanyahu said at an afternoon ceremony.
"Today, too, there are those who threaten to annihilate us -- they haven't succeeded in the past, they won't ever succeed", he said in an apparent reference to Iran.
Israel believes the Islamic republic, which has issued numerous bellicose statements against the Jewish state, is working to achieve military nuclear capabilities.
Most recently last month Iran's supreme leader Ayatollah Ali Khamenei said his country would "annihilate" the Israeli cities of Tel Aviv and Haifa if it comes under attack by the Jewish state.
"If we have no choice, we will grasp our swords and go to battle," Netanyahu said. "Our hand is extended in peace to all nations and states, far and near, but over the centuries we learned that only a strong defence force will ensure that we are not harmed."
Speaking at a later memorial service at the Western Wall in the Old City of Jerusalem, President Shimon Peres said that "Israel's existence is no longer in question. The IDF (Israel Defence Forces) is ready for any scenario, against any enemy."
"Even if the price of peace will be heavy -- we will always be able to bear it."
Speaking after after Peres, army chief Benny Gantz said that "our sword is sharper than ever. Its lethal blade reaches every range. Whoever needs to know, knows -- there is no place or target that the IDF's long arm can't reach."
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"If it seems that the enemy is no longer at our gate -- don't let that quiet mislead you," he said, because "a storm of developing threats and dangers is raging below the surface."
Minute-long sirens sounded nationwide at 8.00 pm (1700 GMT), marking the beginning of the memorial day.
On Monday, further sirens will sound nationwide for two minutes at 11:00 am (0800 GMT), commencing ceremonies at dozens of cemeteries and military memorial sites across Israel.
According to numbers published by the Defence Ministry, since the year 1860 -- when the first Jewish neighbourhood in Jerusalem outside of the Old City was founded and Israel considers the beginning of the Israel-Arab conflict -- 23,085 soldiers and members of the security forces died in the line of duty, including 92 in the past year.
An additional 2,493 civilians were killed in terror attacks in Israel and abroad since 1860, of them 10 in the past year, according to data from the Foreign Ministry.
The army imposed a general closure of the West Bank, beginning with the Sunday evening sirens and ending at midnight Tuesday, a statement said.
Israel regularly shuts down most traffic into and out of the West Bank during Jewish holidays, when the risk of attacks is perceived to be higher.
During the closure, Palestinians in the West Bank are only permitted to leave the territory in cases of urgent humanitarian need.
Memorial Day is followed by Israel's Independence Day, marking 65 years since the declaration of statehood on May 14, 1948, which is celebrated according to the Jewish calendar and this year falls on April 16.
Palestinians mark the occasion on May 15, when they commemorate the Nakba, or "catastrophe" of the creation of Israel, which sparked the exodus of hundreds of thousands of Palestinians.