There is a "narrow window" to prevent famine from spreading further in the Gaza Strip, a top U.N. official said on Sunday, calling on Israel to allow unimpeded aid delivery in the territory, where it is fighting Palestinian militant group Hamas.

According to a global hunger monitor, hundreds of thousands of Palestinians are already experiencing or at risk of famine in areas including Gaza City, the enclave's largest urban center, where Israel has launched a new offensive against Hamas.

Israel, which stopped all aid for 11 weeks from March until mid-May, says it is doing more to let aid enter and be distributed in the enclave to prevent food shortages, though international agencies say far more is needed.