For weeks, Prime Minister Benjamin Netanyahu of Israel has denied that he is trying to block a cease-fire deal in Gaza by hardening Israel’s negotiating position. Mr. Netanyahu has consistently placed all blame for the deadlocked negotiations on Hamas, even as senior members of the Israeli security establishment accused him of slowing the process himself.

But in private, Mr. Netanyahu has, in fact, added new conditions to Israel’s demands, additions that his own negotiators fear have created extra obstacles to a deal. According to unpublished documents reviewed by The New York Times that detail Israel’s negotiating positions, Israel relayed a list of new stipulations in late July to American, Egyptian and Qatari mediators that added less flexible conditions to a set of principles it had made in late May.

Doubts have also been raised about Hamas’s willingness to compromise on key issues, and the group also requested its own extensive revisions throughout the process, while ceding some smaller points in July. But the documents reviewed by The Times make clear that the behind-the-scenes maneuvering by the Netanyahu government has been extensive — and suggest that agreement may be elusive at a new round of negotiations set to begin on Thursday.

Among other conditions, the latest document, presented to mediators shortly before a summit in Rome on July 28, suggested that Israeli forces should remain in control of Gaza’s southern border, a detail that was not included in Israel’s proposal in May. It also showed less flexibility about allowing displaced Palestinians to return to their homes in northern Gaza once fighting is halted.

Some members of the Israeli negotiating team fear that the new additions risked scuppering the deal, according to two senior officials who spoke on the condition of anonymity because they were not authorized to speak to the press.

The Times reviewed the documents and confirmed their authenticity with officials from Israel and other parties involved in the negotiations.