Hamas has replied to a proposal aimed at the release of the remaining hostages in Gaza and a sustained cessation in fighting, Qatari Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani and US Secretary of State Antony Blinken announced Tuesday.

“I would like to inform the media that we have received a reply from Hamas with regards to the general framework of the agreement with regard to hostages,” he said at a press conference alongside Blinken in Doha.

“The reply includes some comments, but in general it is positive. However, given the sensitivity of the circumstances, we will not tackle details,” Al Thani said.

“We are optimistic, and we have delivered the response to the Israeli party,” he said.

The United States is reviewing the response from Hamas “now,” Blinken said.

“I’ll be discussing with the government of Israel tomorrow,” Blinken added.

The top US diplomat reiterated that the proposal that was presented to Hamas was a “serious” one “that was aimed at not simply repeating the previous agreement, but expanding it.”

“There’s still a lot of work to be done, but we continue to believe that an agreement is possible, and indeed essential. And we will continue to work relentlessly to achieve it,” he said at the news conference.

The framework of the proposal was agreed to by negotiators in Paris at the end of last month. CNN previously reported that it would call for a first phase of civilian hostage releases to take place over a six-week pause, with three Palestinian prisoners held by Israel released for each civilian hostage returned from Gaza. That ratio would be expected to go up for Israel Defense Forces soldiers and a longer pause is possible beyond the six weeks for the later phases.

The sides have been unable to reach an agreement to release more hostages since one in November collapsed. That agreement resulted in a weeklong pause in fighting in exchange for the release of more than 100 hostages. Another deal to free the more than 100 who remain would be a major breakthrough at a time of huge tension in the Middle East as concerns grow about a wider regional conflict breaking out.