Rafah residents have reported intense artillery shelling and gunfire in Gaza’s far-southern city after Israel said it had seized a strategic corridor on the Palestinian territory’s border with Egypt.

The Israeli military launched its incursion into Rafah in early May despite international objections over the fate of Palestinian civilians sheltering there.

A strike over the weekend that started a fire and killed dozens in a displacement camp drew a wave of new condemnation, including a social media campaign with the slogan “All eyes on Rafah” that has been shared by tens of millions of users.

Israel said on Wednesday its forces had taken over the 14-kilometre (8.5-mile) Philadelphi corridor on the Gaza-Egypt border, which it suspects was used for weapons smuggling.

Military spokesperson Rear Admiral Daniel Hagari announced Israel had taken “operational control” of the narrow border area, where he said troops had “discovered around 20 tunnels”.

Egypt, a longtime mediator in the conflict that has become increasingly vocal in its criticism of the Israeli operation, has rejected claims of smuggling tunnels running beneath the buffer zone.

“Israel is using these allegations to justify continuing the operation on the Palestinian city of Rafah and prolonging the war for political purposes,” a high-level Egyptian source was quoted as saying by state-linked Al-Qahera News.

Egyptian officials have said a potential Israeli takeover of Philadelphi could violate the two countries’ landmark 1979 peace deal, though there has been no official comment from Cairo since the military’s announcement.

An AFP correspondent reported artillery and gunfire in the Gaza City neighbourhood of Zeitoun, in the territory’s north, where witnesses saw thick plumes of smoke rising over Jabalia refugee camp and Beit Lahiya.

A steady stream of civilians have fled Rafah, transporting their belongings on their shoulders, in cars or on donkey-drawn carts.

Before the Rafah offensive began, the United Nations said up to 1.4 million people were sheltering there. Since then, one million have fled the area, the UN agency for Palestinian refugees, UNRWA, has said.

The Israeli military said on Thursday its forces had attacked more than 50 targets across Gaza the previous day.

Troops found weapons, explosives and tunnel shafts in Rafah, and battled fighters in Jabalia, it said in a statement.

The weekend Israeli attack and ensuing fire, which tore through the camp for displaced Palestinians in Rafah, killed 45 people, according to Gaza officials, and prompted two days of discussions at the UN Security Council.