Israeli Prime Minister Benjamin Netanyahu said the country is "at war" following a surprise large-scale attack by Palestinian militants from Gaza early Saturday morning.

The militant group Hamas, which controls the coastal enclave, fired a barrage of rockets and sent gunmen into Israel in a multi-pronged and unprecedented attack in the long-running conflict between the two sides.

"Citizens of Israel, we are at war -- not in an operation, not in rounds -- at war," Netanyahu said in a video message.

Israeli authorities said that at least 70 people were killed and at least 985 injured and that a number of Israelis had been taken captive by Hamas.

Israel's military responded by launching airstrikes on what it said were Hamas targets in Gaza, where Palestinian officials said at least 198 people were killed and hundreds more injured as a result.

Here's what we know so far.

What happened?

At Around 6:30 a.m. local time on Saturday, when many Israelis were likely to have been asleep, sirens were heard as far north as the Tel Aviv area, east to Beer Sheba, and many other locations in between as rockets flew over Israel.

Militants from Gaza then entered Israeli territory by land, sea and air, with some using paragliders, the Israel Defense Forces (IDF) said. It warned Israelis who live near Gaza to stay in their homes.

Social media video obtained by CNN also showed multiple masked gunmen in a pickup truck driving down a street in the Israeli city of Sderot, which lies close to the Gaza border. Gunfire could also be heard in the video.

The IDF said around 2,200 rockets were fired at Israel. Hamas put the figure at 5,000. To put that in context, some 4,000 rockets were fired from Gaza into Israel during the 50-day war between the two sides in 2014.

Hamas military commander Muhammad Al-Deif called the operation "Al-Aqsa Storm" and said that the assault on Israel was a response to attacks on women, the desecration of the al-Aqsa mosque in Jerusalem and the ongoing siege of Gaza.

Hamas said it captured Israeli soldiers, posting videos of soldiers it allegedly captured on its social media accounts. Videos geolocated and authenticated by CNN suggested that at least one Israeli soldier was taken prisoner by the group.

The group also posted a video allegedly showing a captured Israeli military vehicle. A CNN journalist saw a military Humvee being paraded through Gaza. The IDF declined to comment on the matter. Another video circulating on social media showed a tank on fire near the Gaza border.

How has Israel responded?

In response to the attack, Israel launched "Operation Swords of Iron," striking a number of targets in the Gaza strip. Netanyahu said Israel's response to the Hamas incursion will "exact a huge price" from the militant group.

"The IDF is reinforcing the south and the communities surrounding the Gaza Strip with several operational forces," IDF Spokesperson Rear Admiral Daniel Hagari said in a statement.

The IDF described the attack as "massive." Around noon local time, it said fighting was taking place on the ground in at least seven locations in the country.

IDF spokesperson Lt. Col. Richard Hecht told CNN that "tens of thousands" of Israeli reservists have also been called up to help. He added that Israel is "ready in the north" in case there are attacks from Lebanon or Syria. Lebanese militant group Hezbollah praised the attacks and said it is in contact with Palestinian militant groups, its Al Manar channel said.

Hecht said he hopes "there will be no more live terrorists in Israel" by end of the day.

Inside Gaza, the roar of Israeli warplanes could be heard followed by loud explosions and rising plumes of black smoke.

Palestinians were barred from crossing checkpoints into Jerusalem from the West Bank, and Israel said it will close all educational facilities on Sunday.

How did the two sides get here?

Tensions between Israel and the Palestinians have existed since before the nation's founding in 1948. Thousands of people on both sides have been killed and many more injured in the long-simmering conflict between the two sides over the past few decades.

Violence has been particularly heightened this year. The number of Palestinians -- militants and civilians -- killed in the occupied West Bank by Israeli forces is at its highest in nearly two decades. The same is true of Israelis and foreigners -- most of them civilians -- killed in Palestinian attacks.

Israel and Hamas have been involved in armed conflict dating back as early as the 1987 First Palestinian Intifada, or uprising, against Israel's occupation of the Gaza Strip and the West Bank.

Israel captured Gaza from Egypt in a 1967 war, then withdrew in 2005. The territory, home to some 2 million Palestinians, fell under Hamas' control in 2007 after a brief civil war with Fatah, a rival Palestinian faction which is the backbone of the Palestinian Authority.

After Hamas seized control of Gaza, Israel and Egypt imposed a strict siege on the territory, which is ongoing. Israel also maintains an air and naval blockade on Gaza.

Before Saturday's operation, the last war between Hamas and Israel was in 2021, which lasted for 11 days and killed at least 250 people in Gaza and 13 in Israel.

Saturday's assault occurred on the 50th anniversary of the 1973 war, when Israel's Arab neighbors launched a surprise attack on Israel on Yom Kippur, the holiest day in the Jewish calendar, on October 6, 1973.

What is Hamas?

Hamas is an Islamist organization with a military wing that came into being in 1987, emerging out of the Muslim Brotherhood, a Sunni Islamist group that was founded in the late 1920s in Egypt.

The word "Hamas" is itself an acronym for "Harakat Al-Muqawama Al-Islamia" -- Arabic for Islamic Resistance Movement. the group, like most Palestinian factions and political parties, insists that Israel is an occupying power and that it is trying to liberate the Palestinian territories. It considers Israel an illegitimate state.

Its refusal to recognize Israel is one reason why it has rejected peace talks in the past. In 1993, it opposed the Oslo Accords, a peace pact between Israel and the Palestine Liberation Organization (PLO).

The group presents itself as an alternative to the Palestinian Authority (PA), which has recognized Israel and has engaged in multiple failed peace initiatives with it. The PA is today led by Mahmoud Abbas and is based in the Israeli-occupied West Bank.

Hamas has over the years claimed many attacks on Israel and has been designated as a terrorist organization by the United States, the European Union and Israel. Israel accuses its archenemy Iran of backing Hamas.

How have other countries reacted?

Western states condemned the Hamas attack and pledged support for Israel while Arab states, including those that have recognized Israel, called for calm.

United States President Joe Biden spoke to Israeli Prime Minister Benjamin Netanyahu on Saturday and said that Washington "unequivocally condemns this appalling assault against Israel by Hamas terrorists from Gaza."

"I made clear to Prime Minister Netanyahu that we stand ready to offer all appropriate means of support to the government and people of Israel," he said.

German President Frank-Walter Steinmeier spoke to Israeli President Isaac Herzog on Saturday, saying Israel "must defend itself against a brutal terror."

Saudi Arabia, which is holding talks with the US to potentially normalize relations with Israel, said it is following closely the "unprecedented" situation and called on "both sides to immediately stop the escalation," according to a statement by the Saudi foreign ministry on X.

The UAE, which recognized Israel in 2020, called for "the exercise of maximum restraint and an immediate ceasefire to avoid dangerous repercussions."