The Palestinian Red Crescent said Sunday that Israeli forces were besieging two hospitals in southern Gaza, days after the army began targeting Hamas in and around the territory's biggest medical centre.

Israel has mounted several raids at and near hospitals in Gaza since the war began last October, claiming that fighters are operating in medical complexes -- a charge denied by the Palestinian militant group Hamas.

Military vehicles approached Nasser and Al-Amal hospitals in southern Gaza's Khan Yunis as heavy bombardment and gunfire echoed in the area, the Red Crescent said.

The medical organisation said a volunteer worker at the hospital was killed by Israeli gunfire early Sunday. AFP has asked the military for comment.

The Red Crescent said messages broadcast from drones demanded that everyone in Al-Amal leave naked, while forces blocked the gates of the hospital with dirt barriers.

"All of our crews are currently under extreme danger and cannot move at all," the group added.

Israel's military said it began an operation in the Al-Amal neighbourhood "in order to continue dismantling terrorist infrastructure and eliminating terrorist operatives in the area".

The military said the operation began with air force strikes on approximately 40 targets, including military compounds, tunnels and other "terror infrastructure".

Israeli forces started a major operation early Monday that is still going on, saying they were targeting Hamas fighters in and around Gaza's largest hospital, Al-Shifa.

The raid, which Israel vowed will continue until the last fighter is in its hands, has killed some 170 militants, according to the military.

The military previously raided the facility last November, sparking international criticism.

Israel has also previously carried out operations around Al-Amal, with the Red Crescent in February saying the military had engaged in a multi-day siege of the facility.