He announced that Mr Obama had earmarked the $20.3m for aid to Gaza on top of $40m allocated to humanitarian programmes there since hostilities broke out in late December.
"The United States remains committed to actively and aggressively seeking a lasting peace between Israel and the Palestinians as well as between Israel and its Arab neighbours," he said.
"The tragic violence in Gaza and in south Israel offers a sobering reminder of the very serious and difficult challenges and, unfortunately, the setbacks that will come.
"It is important to consolidate a sustainable and durable ceasefire while addressing immediately humanitarian needs," he said.
On Thursday Mr Mitchell met Palestinian Authority President Mahmoud Abbas.
Following the meeting he called for Israel to open the crossing points into Gaza and for the Palestinian Authority to participate in a border regime in Gaza that prevents, Hamas, the militant group that controls the territory, from rearming.
Many see Mr Mitchell's presence as a sign that the US is re-engaging - but few expect to see much progress soon, as Israel is in an election campaign with the right-wing Likud ahead in the polls, BBC Jerusalem correspondent Bethany Bell says.
On Thursday the United Nations launched an appeal for $613m to help people affected by Israel's three-week military offensive in the Gaza Strip.
The offensive, which ended on 18 January, killed about 1,300 Palestinians, of whom 412 were children; 21,000 homes were destroyed or badly damaged.
Thirteen Israelis were killed during the three weeks of violence.
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