(NewsNation) — Israel has vowed a “complete siege” of Gaza after an attack carried out by Hamas that left more than 900 Israelis dead.

Maj. Ben Wahlhaus, spokesman for the Israel Defense Forces, says the military’s highest priority is to drive Hamas forces out of Israel and stop the attacks.

“We have the south under control now, we have the border closed, there are no longer these terrorists streaming across the border, our forces are still going house by house making sure none of them are left,” Wahlhaus said Monday on “CUOMO.”

Hamas and other militants in Gaza say they are holding more than 130 soldiers and civilians snatched from inside Israel. Hamas has vowed to start executing them if Israel continues to strike targets in Gaza.

“These are challenging circumstances for us to fight in, but that’s our highest priority at the moment — to stop those attacks on Israel and on Israel’s civilian population,” Wahlhaus said.

Israeli tanks and drones were deployed to guard breaches in the Gaza border fence to prevent new incursions. Thousands of Israelis were evacuated from more than a dozen towns near Gaza, and the military summoned 300,000 reservists — a massive mobilization in a short time.

The moves, along with Israel’s formal declaration of war Sunday, pointed to Israel increasingly shifting to the offensive against Hamas, threatening greater destruction in the densely populated, impoverished Gaza Strip.

The Associated Press contributed to this report.