WASHINGTON - U.S. Gaza aid envoy David Satterfield is set to step down shortly and will be replaced by former senior United Nations official Lise Grande, two sources familiar with the issue told Reuters on Wednesday.

Satterfield was appointed six months ago as the U.S. special envoy for Middle East humanitarian issues with a specific focus on leading the U.S. response to the humanitarian crisis in the Gaza Strip.

Grande is currently head of the independent U.S. Institute of Peace. She previously worked for the United Nations for more than 25 years, a career that included running aid operations in Yemen, Iraq and South Sudan.

The United Nations has long complained of obstacles to getting aid in and distributing it throughout Gaza in the six months since Israel began an aerial and ground offensive against Gaza's ruling Islamist militant group Hamas.

Israel's military campaign has reduced much of the territory of 2.3 million people to a wasteland with an unfolding humanitarian disaster since October, when Hamas ignited war by storming into southern Israel.

Satterfield said on Tuesday that Israel has taken significant steps in recent weeks on allowing aid into Gaza, but considerable work remained to be done as the risk of famine in the enclave is very high.

A U.N.-backed report published in March said that famine was imminent and likely to occur by May in northern Gaza and could spread across the enclave by July. REUTERS