U.S. President Joe Biden spoke on Sunday with Qatar's Emir Sheikh Tamim bin Hamad Al Thani about developments in Gaza and "urgent ongoing efforts" to secure the release of hostages being held by the Hamas militant group, the White House said.

Biden "unequivocally" condemned the holding of hostages by Hamas, including many young children, one of whom is a 3-year old American citizen whose parents were killed by the group on October 7th, the White House said in a statement.

"The two leaders agreed that all hostages must be released without further delay," the statement said.

Hamas fighters surged across the border from Gaza into Israel on Oct.7, killing about 1,200 people and taking more than 200 hostages, according to Israeli officials. Only four hostages have been released to date.

The Israeli bombardment of Gaza has since killed more than 11,000 Palestinians, around 40% of them children, according to counts by health officials in the Hamas-ruled territory.

Reuters last week reported that Qatar, where several political leaders of Hamas are based, has been leading mediation efforts between Hamas and Israeli officials over the hostages.

Biden's national security adviser, Jake Sullivan, told CNN's "State of the Union" earlier on Sunday that "active, intensive negotiations" were underway involving Israel, Qatar, Egypt and the United States on securing the release of more hostages, but it was not clear if all were alive.

"The goal here is to do what is necessary at the negotiating table to ensure that we get the safe return of all of the hostages, including the Americans," Sullivan told CNN, noting that nine Americans were missing, along with one person with permanent resident status in the United States.

"We don't know the status, whether they are alive or whether they have passed away, but we are looking to get the safe recovery of all of those individuals," he said. Sullivan said he would meet with the families of the American hostages this week.

A U.S. official said Brett McGurk, Biden's senior Middle East adviser, will visit Israel on Tuesday and meet Israeli Prime Minister Benjamin Netanyahu, with further visits planned in Brussels, Saudi Arabia, Jordan and Qatar.

Qatar's government earlier said Al Thani had stressed the need for an immediate ceasefire in Gaza and the permanent opening of the Rafah crossing into Egypt in the call with Biden.

Washington has rejected calls from Arab leaders and others for it to insist that Israel halt its assault on the Hamas-controlled Gaza strip.

The White House statement made no mention of any discussion of a ceasefire, saying only that the leaders talked about the need "to protect innocent civilians and ongoing efforts to increase the flow of humanitarian assistance into Gaza."

Biden also affirmed his vision for a future Palestinian state "where Israelis and Palestinians can live side by side with equal measures of stability and dignity," the White House said, adding that Hamas had long been an impediment to that.

It said the two leaders agreed to continue their efforts to advance a shared vision for a more peaceful, secure, prosperous, and stable Middle East region.