"The Al-Qassam Brigades engage in fierce clashes with the invading (Israeli) enemy forces in eastern Rafah," said the brigades in a brief statement.
A separate group, the Al-Quds Brigades, the armed wing of the group Islamic Jihad, also announced that its forces are engaged in fierce clashes with Israeli forces in eastern Rafah.
Avichay Adraee, a spokesman for the Israeli army, said the Israeli army is conducting a surprise attack against what he called "Hamas targets” in the eastern Rafah area.
Earlier on Tuesday, Israeli forces seized control of the Rafah border crossing linking Gaza with Egypt, closing it to all traffic.
On Monday, Israeli forces issued evacuation orders for Palestinians in eastern Rafah, in a move widely seen as a prelude to Israel's long-feared attack on the city, which is home to some 1.5 million displaced Palestinians.
For seven months, Israel has pounded the Gaza Strip in retaliation for an Oct. 7 attack by Hamas which killed about 1,200 people. Nearly 34,800 Palestinians have since been killed in Gaza, the vast majority of them women and children, and over 78,000 others injured, according to Palestinian health authorities.
Vast tracts of Gaza currently lay in ruins, pushing 85% of the enclave’s population into internal displacement amid a crippling blockade of food, clean water, and medicine, according to the UN.
Israel stands accused of genocide at the International Court of Justice. An interim ruling in January said it is "plausible" that Israel is committing genocide in Gaza and ordered Tel Aviv to stop such acts and take measures to guarantee that humanitarian assistance is provided to civilians in Gaza.