Hundreds of people have died and thousands more are injured in Israel and Gaza after Hamas militants fired rockets from Gaza into Israel Saturday, Israeli authorities said.

The Israeli Defense Forces have declared "a state of alert for war," according to a statement issued by the IDF early Saturday morning.

Is there a travel advisory to Israel?

The U.S. State Department is advising citizens to exercise increased caution if traveling to Israel or West Bank due to "terrorism and civil unrest," and it currently has a "do not travel" advisory for Gaza.

The department said in an update Sunday that the situation "remains dynamic; mortar and rocket fire may take place without warning."

Is travel to Israel suspended?

The Federal Aviation Administration on Saturday urged U.S. airlines and pilots to "use caution" when flying in Israeli airspace.

The agency issued a NOTAM, or Notice to Air Missions, to pilots following the unrest that reads, in part, "potentially hazardous situation" and "operators are advised to exercise extreme caution."

Which airlines have canceled flights?

Several airlines on Saturday temporarily suspended flights to and from Tel Aviv.

United Airlines said it will suspend operations to Israel, telling ABC News: "The safety of our customers and crew is our top priority. We are closely monitoring the situation and we are adjusting flight schedules as required."

American Airlines also temporarily suspended operations, saying in a statement: "We will continue to monitor the situation with safety and security top of mind and will adjust our operation as needed."

Delta Air Lines canceled scheduled flights into and out of Tel Aviv this weekend.

The airline said it's working to "safely transport Delta people back to the U.S. and will work with the U.S. government as needed to assist with the repatriation of U.S. citizens who want to return home."

Both United and Delta announced travel waivers following the attacks.

Flights out of Tel Aviv

On Sunday, flights were still arriving and departing from Tel Aviv on Sunday, according to flight tracker FlightAware.

How to get out of Israel

U.S. citizens in Israel "should follow local government advice to increase their security awareness and remain safe," the State Department said. Citizens who need assistance should fill out the crisis intake form to contact their nearest U.S. embassy or consulate

"U.S. citizens who wish to leave and can do so safely are advised to check the status of the border crossings or verify flights have not been canceled before heading to the Ben Gurion Airport," the department said.

ABC News' Amanda Maile contributed to this report.