Israeli troops mass along Gaza border amid tension

One rocket fired from the Palestinian enclave crashed into a building near Israel's commercial capital of Tel Aviv, injuring five Israelis, police said. Sirens blared in cities across southern Israel, sending thousands running for shelters.

In renewed air strikes on Thursday, Israel destroyed a six-storey residential building in the heart of Gaza City. One man was killed by an Israeli missile fired east of Khan Younis in southern Gaza, medics said.

A wave of violence between Jewish Israelis and the country's Arab minority also spread in several Israeli cities.

At least 72 people have been killed in Gaza since violence escalated on Monday, medics said, further straining hospitals already under heavy pressure during the COVID-19 pandemic. Seven people have been killed in Israel, its military said.

Israel has prepared combat troops along the Gaza border and was in "various stages of preparing ground operations", a military spokesman said, a move that would recall similar incursions during Israel-Gaza wars in 2014 and 2008-2009.

"The Chief of Staff is inspecting those preparations and providing guidance," Lieutenant Colonel Jonathan Conricus said.

Health authorities in Gaza said they were investigating the deaths of several people overnight who they said may have inhaled poisonous gas. Samples were being examined and they had yet to draw any final conclusions, they said.

Amid fears the violence could spiral further out of control, Washington planned to send an envoy, Hady Amr, for talks with Israel and Palestinians.

U.S. President Joe Biden said he hoped fighting "will be closing down sooner than later". A British minister urged Israel and Hamas to "take a step back" from the escalation.

Israeli Prime Minister Benjamin Netanyahu has vowed to "continue acting to strike at the military capabilities of Hamas" and other Gaza groups.