Israel looks to be gearing up for an invasion to crush Hamas, but another enemy is stirring up trouble

• Israel appears to be gearing up for a ground invasion of Gaza after Hamas staged a brutal attack.
• But attention is also being directed to Israel's border with Lebanon, where fighting has broken out.

As Israeli forces mass near the Gaza Strip ahead of what many say is an imminent ground invasion, dangerous fighting in the north threatens to turn the war with Hamas into a larger conflict.

Israel officially declared war against Hamas on Sunday, a day after the militant group carried out a multi-front surprise attack across the country that has killed at least 800 people — mostly civilians and some foreign nationals — and wounded thousands more. In response to the massacre, Israel Defense Forces (IDF) fighter jets immediately began a widespread bombing campaign of what it said were Hamas targets across the Gaza Strip.

The ongoing operation, known as Swords of Iron, has all the markings of a looming ground invasion, as Israeli forces and firepower gather near the border with Gaza, a densely populated sliver of land that's home to roughly 2 million people. Israeli Prime Minister Benjamin Netanyahu told President Joe Biden on Sunday that his military has no choice but to invade Gaza and that there will be no negotiations with Hamas, Axios reported.

"Our job is to make sure that at the end of this war, Hamas will no longer have any military capabilities to threaten Israeli civilians with," an IDF spokesperson said on Sunday. "And in addition to that, we are also to make sure that Hamas will not be able to govern the Gaza Strip."

The IDF announced on Monday that more than 300,000 reserve troops have been mobilized. This "is more than we have ever done before in such a short period of time. And that should indicate the severity of the situation from our perspective," an IDF spokesperson said, adding that troops have been dispatched to southern and northern Israel.

Yoav Gallant, Israel's defense minister, also said on Monday that he ordered a "complete siege" on Gaza, cutting off electricity, food, fuel, and water. Heavy armor — like tanks — was also spotted en route to Gaza.

But as a potential ground invasion appears to be on the horizon, Israel has also been forced to divert some attention to its northern border with Lebanon, where Hezbollah — an Iran-backed group that, like Hamas, is designated as a terrorist organization by the US State Department — has been exchanging fire with the IDF.

On Sunday, the United Nations Interim Force in Lebanon (UNIFIL), a decades-old peacekeeping mission, said it detected several rockets fired from Lebanon into Israel, which then responded with artillery strikes. The following day, UNIFIL said it detected explosions in southwestern Lebanon, while the IDF said its forces killed several "militants" who crossed into Israel from Lebanon and its helicopters attacked Lebanese territory in response.

"While we are working to gather more information, UNIFIL Head & Force Commander Maj Gen Lázaro is in contact with the involved parties, urging them to exercise maximum restraint & utilize UNIFIL's liaison and coordination mechanisms to prevent further escalation and loss of life," the peacekeeping mission said on Monday.

The recent fighting between Israel and Hezbollah — which is allied with Hamas — has stoked fears that the war could turn into a wider regional conflict if a second front opens up in the north. According to the Center for Strategic and International Studies, a Washington-based think tank, Hezbollah is the "world's most heavily armed non-state actor," outfitted with a massive stockpile of artillery rockets, ballistic missiles, anti-tank missiles, and anti-ship missiles.

Anti-ship missiles in particular could pose a headache for the Pentagon, which has dispatched its most advanced aircraft carrier and its heavily armed strike group to Israel's coast.

US Defense Secretary Lloyd Austin said the movement of the USS Gerald R. Ford Carrier Strike Group — which consists of several warships able to launch guided missiles — comes alongside the transfer of weaponry to Israel, and the movement of additional fighter jets to the area. Hezbollah has already threatened that US assets will become targets if Washington directly intervenes.

"Strengthening our joint force posture, in addition to the material support that we will rapidly provide to Israel, underscores the United States' ironclad support for the Israel Defense Forces and the Israeli people," Austin said on Sunday. "My team and I will continue to be in close contact with our Israeli counterparts to ensure they have what they need to protect their citizens and defend themselves against these heinous terrorist attacks."

Meanwhile, as Israel gathers its ground forces, IDF fighter jets continue to bombard the Gaza Strip for a third consecutive day, striking what the military said are thousands of Hamas targets. Gaza's Ministry of Health said as of Monday afternoon that over 500 Palestinians were killed and nearly 3,000 more injured.

It remains to be seen how an invasion might play out, should the IDF carry one out, although it is likely to be a costly campaign in brutal environment with intense urban combat. Israel also has to contend with the issue that there are dozens of hostages who were kidnapped by Hamas during Saturday's surprise attack and are believed to be held captive within Gaza, which could complicate operations.