US President Joe Biden warned on Friday that it would be "tough" to secure a ceasefire between Israel and Hamas by the Muslim holy month of Ramadan.

"It's looking tough," Biden told reporters when asked if a deal to halt the five-month-old conflict could be achieved by Ramadan, which is due to start as early as Sunday depending on the sighting of the moon.

Biden added that "I sure am" worried about the possibility of violence in Israeli-annexed east Jerusalem as Ramadan approaches, adding to a similar warning earlier this week.

Hamas's armed wing on Friday urged supporters to mobilise towards the Al-Aqsa mosque compound in east Jerusalem, a flashpoint for violence during Ramadan in past years.

It also said there would be no compromise on the movement's demand that Israel withdraw from Gaza to secure the release of hostages seized by Hamas.

The Israel-Hamas war was triggered by the Palestinian militants' unprecedented attack on southern Israel on October 7. (AFP)