Hamas must release more hostages to position itself for a significant increase in aid to Gaza and a pause in fighting, one of the U.S.’ top Middle East envoys said Saturday.

“The surge in humanitarian relief, the surge in fuel, the pause in fighting will come when hostages are released,” said Brett McGurk, who is President Joe Biden’s coordinator for the Middle East and North Africa.

McGurk, speaking at the IISS Manama Dialogue, a regional security conference in Bahrain, said the U.S.’ approach has helped hostage negotiations so far.

Hamas, which the U.S. and Europe designate a terrorist organization, swarmed southern Israeli communities on Oct. 7, killing about 1,200 people and taking 240 back to Gaza as hostages. Israel’s responded with massive airstrikes and a ground offensive on the enclave, which the Hamas-run government says have killed more than 12,000 people.

Only four of the hostages have been released, including two American citizens. Israel has freed another, while a few are known to have died, according to Hamas and Israeli officials.

Hamas has lost contact with groups assigned to guard some of the hostages, Abu Obaida, a spokesman for Hamas’ military wing, said Saturday. “The fate of the captives and captors is still unknown,” he said in a statement.

Biden spoke to Qatar’s ruling emir, Sheikh Tamim bin Hamad Al Thani, on Friday about trying to ensure Hamas lets go of more people. Qatar hosts members of Hamas’ political leadership and has been key to the hostages negotiations, acting as a mediator along with other Arab countries such as Egypt.

The hostage talks have been fraught, with Israel and Hamas blaming each other for some of them breaking down.

More aid has gone into Gaza in recent weeks, mostly food and medicine via the Rafah crossing with Egypt. Fuel was sent in on Wednesday for the first time since the conflict erupted. Israel had been reluctant to allow that, saying Hamas would use it for military operations. But it has come under more pressure, including from the U.S., as Gaza’s hospitals and water plants run out of fuel for generators.