TEL AVIV — Israel on Wednesday announced it had begun criminal investigations into five instances of possible military misconduct in the 50-day Gaza war, an implicit acknowledgment of sensitivity to the widespread criticism, even among allies like the United States, that Israeli forces had used excessive firepower in a number of highly publicized assaults in the Palestinian territory.

The announcement, conveyed at a briefing by the Israeli military, came only two weeks after a cease-fire in the conflict, an unusually speedy response. But critics, including human rights advocates in Israel, said it remained to be seen whether the investigations would yield significant criminal indictments and punishments.

Some said the timing of the inquiries appeared to be an attempt by the Israeli government to pre-empt the impact of international investigations into allegations of possible Israeli war crimes committed in Gaza. They also pointed out that the cases, opened by Israel’s Military Advocate General Corps, included obvious episodes that had already drawn condemnation.

One prominent Israeli human rights group, B’Tselem, refused to participate in the investigations and said history showed that the Israeli military could not possibly conduct a credible prosecution of itself.