(Reuters) - U.S. Vice President Kamala Harris on Sunday demanded Palestinian militant group Hamas agree to an immediate six-week ceasefire while forcefully urging Israel to do more to boost aid deliveries into Gaza, where she said innocent people were suffering a "humanitarian catastrophe."

In some of the strongest comments by a senior leader of the U.S. government to date on the issue, Harris pressed the Israeli government and outlined specific ways on how more aid can flow into the densely-populated enclave where hundreds of thousands of people are facing famine, following five months of Israel's military campaign.

"Given the immense scale of suffering in Gaza, there must be an immediate ceasefire," Harris said at an event in Selma, Alabama.

"There is a deal on the table, and as we have said, Hamas needs to agree to that deal. Let's get a ceasefire."

"People in Gaza are starving. The conditions are inhumane and our common humanity compels us to act...The Israeli government must do more to significantly increase the flow of aid. No excuses," she said.

On Sunday, a Hamas delegation had arrived in Cairo for the latest round of ceasefire talks, billed by many as the final possible hurdle for a truce, but it was unclear if any progress was made. Israeli newspaper Yedioth Ahronoth's online version reported that Israel boycotted the talks after Hamas rejected its demand for a complete list naming hostages who are still alive.

Washington has insisted the ceasefire deal is close and has been pushing to put in place a truce by the start of Ramadan, a week away. A U.S. official on Saturday said Israel has agreed on a framework deal.

An agreement would bring the first extended truce of the war, which has raged for five months so far with just a week-long pause in November. Dozens of hostages held by Hamas militants would be freed in return for hundreds of Palestinian detainees.

One source briefed on the talks had said on Saturday that Israel could stay away from Cairo unless Hamas first presented its full list of hostages who are still alive. A Palestinian source told Reuters that Hamas had so far rejected that demand.

After the Hamas delegation arrived, a Palestinian official told Reuters the deal was "not yet there". There was no official comment from Israel.

In past negotiations Hamas has sought to avoid discussing the wellbeing of individual hostages until after terms for their release are set.

In other diplomatic moves, Israeli war cabinet member Benny Gantz will meet Harris at the White House on Monday and U.S. Secretary of State Antony Blinken in Washington on Tuesday. U.S. envoy Amos Hochstein will visit Beirut on Monday to pursue efforts to de-escalate the conflict across the Lebanese-Israeli border.