NATO countries on Thursday told Israel's defence minister they stood by his country after the attack by Hamas, but urged his forces to respond with "proportionality", the alliance said.

Israeli Defence Minister Yoav Gallant briefed his counterparts from the US-led military alliance via videolink as his country's military carries out a bombing campaign after Islamist militants killed over 1,200 people, mostly civilians.

"Secretary General Jens Stoltenberg said that NATO condemned the terrorist attacks in the strongest possible terms, adding: 'Israel does not stand alone'," NATO said in a statement.

"Allies expressed solidarity with Israel, making clear that it has the right to defend itself with proportionality against these unjustifiable acts of terror."

NATO countries "called for Hamas to immediately release all hostages, and for the fullest possible protection of civilians. Allies also made clear that no nation or organization should seek to take advantage of the situation or to escalate it."

The statement added that "a number of NATO allies made clear that they are providing practical support to Israel as it continues to respond to the situation".

In Gaza, officials have reported more than 1,200 people killed in Israel's uninterrupted campaign of air and artillery strikes, while the UN said more than 338,000 people have been displaced.

US President Joe Biden — who has strongly backed Israel and started sending military aid — has cautioned that Israel must, despite "all the anger and frustration … operate by the rules of war".

British Defence Secretary Grant Shapps insisted Thursday that Israel was "going after the terrorists" in Gaza.

"They are not by design attacking civilians," he told journalists at NATO headquarters.

"That's a very, very important, critical difference that I think the whole world needs to understand."