The Israeli military said its forces were carrying out an operation at Gaza's biggest hospital, Al Shifa.
The Israeli military said it was carrying out an operation against Hamas in the Gaza Strip's Al Shifa hospital on Wednesday and urged all members of the militant group in the hospital to surrender.
Less than an hour earlier, a Gaza health ministry spokesman said Israel had told officials in the enclave that it would raid the Shifa hospital complex "in the coming minutes."
In a statement, the Israel Defence Forces (IDF) said: "Based on intelligence information and an operational necessity, IDF forces are carrying out a precise and targeted operation against Hamas in a specified area in the Shifa Hospital."
The military added: "The IDF forces include medical teams and Arabic speakers, who have undergone specified training to prepare for this complex and sensitive environment, with the intent that no harm is caused to the civilians."
Israel has said that Hamas has a command centre underneath Al Shifa hospital, the biggest in Gaza, and uses the hospital and tunnels underneath to conceal military operations and to hold hostages. Hamas denies it.
The US said on Tuesday that its own intelligence supported those conclusions.
Five weeks after Israel swore to destroy Hamas in retaliation for militants' cross-border assault, the fate of Al Shifa has become a focus of international alarm because of worsening conditions in the facility.
Medical staff have said the hospital is barely functioning due to Israeli attacks and a lack of fuel to power generators.
Israeli forces have waged fierce street battles against Hamas fighters over the past 10 days before advancing into the centre of Gaza City and surrounding Al Shifa
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