Israel sent tanks into eastern Jabalia in the northern Gaza Strip early on Sunday, after a night of heavy aerial and ground bombardments.
Late on Saturday, the Israeli military said forces operating in Jabalia are preventing Hamas, which controls Gaza, from re-establishing its military capabilities there.
"We identified in the past weeks attempts by Hamas to rehabilitate its military capabilities in Jabalia. We are operating there to eliminate those attempts," said Rear Admiral Daniel Hagari, Israel's military spokesperson, during a briefing to reporters.
Hagari also said that Israeli forces operating in Gaza City's Zeitoun district.
The army sent tanks back into Al-Zeitoun, an eastern suburb of Gaza City, as well as Al-Sabra.
The army had claimed to have gained control of most of these areas months ago.
Hamas, which still has several thousand men, is attempting to reestablish itself in certain areas of Gaza.
This demonstrates the organization's unwillingness to engage in a ceasefire, release hostages, or surrender, which would lead to an end to the conflict and civilian casualties.
By Nidal al-Mughrabi and Mena Today