The pace of Palestinian civilians fleeing the combat zone in northern Gaza has picked up as Israel’s air and ground campaign there intensifies. The UN Office for the Coordination of Humanitarian Affairs said Wednesday that about 15,000 people fled on Tuesday, compared to 5,000 on Monday and 2,000 on Sunday.

The densely populated northern area of Gaza, specifically Gaza City and adjacent crowded urban refugee camps, are the focus of Israel’s campaign to crush Hamas, the militant group that has ruled Gaza for 16 years.