Asked by reporters at the White House -- where Biden was arriving for a meeting with US negotiators -- if he thought the Israeli leader was doing enough on the issue, the president responded: "No."

Biden's meeting with the negotiators on the captive-release deal comes after the deaths on Saturday of six captives in Gaza, including an American citizen.

The president said negotiators were "very close" to a final proposal to be presented to Israel and Hamas.

Biden's schedule was revised to make time for the White House meeting, which was also to be attended by Vice President Kamala Harris, who is running to succeed him in November's presidential election.

A White House statement said he and Harris would meet the US team negotiating the deal. 

The meeting would take place to "discuss efforts to drive towards a deal," according to the statement. 

The United States, along with fellow mediators Egypt and Qatar, has spent months pushing for a captive-prisoner exchange and ceasefire in the war in Gaza.

Militants seized 251 captives, 97 of whom remain in Gaza, including 33 the Israeli military says are dead.

Scores of captives were released during a one-week truce in November.

An Israeli court on Monday ordered a halt to a strike called by the country's largest union aimed at ramping up pressure on Netanyahu's government to secure the release of the remaining captives.

Captive relatives and advocates have accused Netanyahu's administration of not doing enough to bring the captives back alive, and have called for an immediate ceasefire.

More than 40,786 Palestinians have been killed in Israel's war on the Gaza Strip.

Most of the dead are women and children according to the UN human rights office.