Hamas fighters are believed to be "still hiding" in some communities in southern Israel even after the Israeli military took back control, according to Israel Defense Forces spokesman Maj. Doron Spielman.

"We are in control of the communities, but we actually assume that there are Hamas terrorists that are still hiding in these areas, including in the road where we are now," Spielman told ABC News during an interview Monday in Sderot, Israel. "In all these communities, we've seen terrorist come out of hiding. Just yesterday, they took over an ambulance."

"We're still being very, very careful," he added. "This is a war zone with active terrorists that are operating here."

Sderot is a southwestern Israeli city located near the county's border with the Hamas-ruled Gaza Strip. A police station there was stormed by Hamas fighters on Saturday as part of the militant group's wider incursion, leaving at least six Israeli police officers dead. The IDF then bombed the police station with the Hamas fighters inside, demolishing it.

Hamas fighters and other Palestinian militants are "striking strategic locations" along the border fence, allowing them to drive through in pickup trucks, Spielman said. Civilians in some of the local communities have been ordered to evacuate, while others have left voluntarily, according to Spielman.

"We do have a lot of ground troops in this area. We have a lot of tanks. We have, in addition, artillery. And we're prepared forever for anything," he said. "And if it happens, the next stage, it's going to happen here because this is the area that was the flashpoint and this is the area we're going to be presenting ourselves and finishing this battle. We, of course, have no choice but to finish."

When asked about the mounting casualties of Palestinian civilians in Gaza as a result of the IDF's retaliatory airstrikes, Spielman said: "We always try to avoid civilian casualties. However, I would say that this is war and our first priority here is to destroy Hamas."

-ABC News' Angus Hines and Ian Pannell

The Israel Defense Forces said Tuesday morning that its fighter jets had struck more than 200 "terror targets" in the Gaza Strip overnight.

All targets were located in the Rimal neighborhood of Gaza City and the southern city of Khan Yunis, which the IDF said are both used as "terror hubs" for Gaza's militant rulers Hamas and that "a large number of terror attacks against Israel are directed there."

Among the targets struck were a Hamas weapons storage site and a Hamas operational command center, both located inside a mosque, according to the IDF.

-ABC News' Jordana Miller

The FBI said it is working "aggressively" to investigate reports of Americans who have been impacted by the Hamas attacks on Israel.

"We are closely coordinating with our counterparts in the region as well as other international partners," the FBI said in a statement posted on X, the platform formerly known as Twitter, on Monday.

The statement continued: "Through our Legal Attache' office in Israel, FBI personnel are working with our partners on the ground to locate and identify any impacted Americans. Reports of deceased, injured or missing Americans are being treated with the utmost urgency and aggressively investigated. The FBI's Victim Services Division is coordinating with the Department of State to assist, as necessary, with family engagement."

The Israel Defense Forces will fight this war "as long as it takes," spokesperson Lt. Col. Res. Jonathan Conricus told ABC News in an interview on Monday.

"The goal that we have been given so far by the Israeli government is to make sure that Hamas doesn't have any military capabilities that they can use to threaten or murder Israeli citizens. That means to eradicate their ability to terrorize Israelis," Conricus said.

"That's what we've been tasked to do so far -- that may change, expand, and include political things as well as in their ability to govern, but as of now, what we're focusing on with the aerial strikes that are ongoing and the preparations of the other troops around the Gaza Strip is to strip Hamas of all of their military capabilities," he added.

The IDF is looking at "difficult and hard passes ahead," but Saturday's attack by Hamas fighters was a "watershed moment" that has fundamentally changed how the IDF responds, according to Conricus.

"Bottom line, what was true and perhaps worked for years before, won't cut the situation now and we are moving forward," he said.

In addition, 300,000 IDF reservists who were called up are "now in southern Israel," according to Conricus.

"We have mobilized our troops before -- the second Lebanon war comes to mind," he added. "But this is definitely very, very significant."

-ABC News' Matt Gutman, Ellie Kaufman and Becky Perlow

A State Department official said Monday night that the department has offered 4,000 American citizens and their immediate family members help to depart Israel via government-organized transportation since Friday.

“Since Oct. 13, we have augmented the limited commercial flight availability by offering more than 4,000 seats on U.S. government-chartered transport by air and sea to U.S. citizens and their immediate family members,” one official said. “We have communicated the availability of departure assistance options for U.S. citizens via targeted, individualized messaging as well as via broad public messaging.”

Departing flights, though, were not nearly at capacity, the official said.

“The departure options we have offered have generally departed at half capacity or less. Nearly 1,000 U.S. citizens and their immediate family members have departed on U.S. government-chartered transport,” an official said.

The official added that 3,000 other American citizens have told the State Department that they were able to leave Israel and the West Bank on their own.

-ABC News’ Shannon Crawford