Jerusalem (CNN) -- Israel and Hamas both failed to investigate serious violations of the laws of war during the Israeli incursion into Gaza in 2008 and early 2009, according to a new report released Sunday by Human Rights Watch.
"Thoroughness and impartiality" of Israeli investigations remain in doubt, while the Palestinian militant group Hamas "has taken no meaningful steps to investigate and punish those who violated the laws of war," said the 62-page report, titled "Turning a Blind Eye."
The report calls on Israel to investigate three main issues regarding the conflict: Israel Defense Forces' use of white phosphorus munitions in populated areas; the killing of civilians with drone-launched missiles; and the killing of civilians who were waving white flags.
According to Human Rights Watch, an international human rights organization, 53 civilians were killed in 19 incidents in which Israeli forces appear to have violated international laws of war. Six of those, according to the group, involved the unlawful use of white phosphorus munitions. Six others were attacks by drone-launched missiles that killed civilians, the group alleged, and seven involved soldiers shooting civilians who were in groups holding white flags.
In the midst of the three-week incursion, in January 2009, Human Rights Watch said Israel appeared to be using white phosphorus as an "obscurant," a chemical used to hide military operations.
Such a use is permitted "in principle" under the laws of war, HRW said at the time. "However, white phosphorus has a significant, incidental, incendiary effect that can severely burn people and set structures, fields, and other civilian objects in the vicinity on fire." The potential for harming civilians was magnified by Gaza's high population density, the group said.
"Yet again, Human Rights Watch got their facts and figures wrong on their way to hasty conclusions," said Yigal Palmor, spokesman for the Israeli Foreign Ministry. "They have displayed in this and in previous reports [a] lack of professional integrity and they are therefore not to be taken as an authority to judge and evaluate IDF operations.
"Israel will continue to cooperate in full transparency with the U.N. as it has always done, and opportunistic kibitzing by self-appointed watchers does not help," Palmor said.
Hamas and other Palestinian armed groups are blamed for "firing thousands of rockets into Israel since 2001, killing 15 civilians, wounding many more, and posing an ongoing threat to the nearly 800,000 Israeli civilians who live and work in the weapons' range," the group said. During the 22 days of fighting in December 2008 and January 2009, "rocket attacks killed three Israeli civilians, wounded scores more, and caused damage to civilian infrastructure," HRW said.
Although international law does not specify a single standard for the conduct of investigations, "basic justice principles necessitate that investigations be prompt, thorough and impartial," and that any resulting prosecutions be independent, the report said.
The organization called for independent investigations in both Israel and Gaza in order to hold perpetrators accountable and provide civilian victims with redress. Influential governments and international bodies are also urged to renew their pressure on Israel and Hamas to conduct domestic investigations that are prompt, thorough and impartial, the group said.
In February, Human Rights Watch said in a statement that Israel had not demonstrated it would conduct thorough and objective investigations.
In September, the United Nations Human Rights Council released a report by noted South African jurist Richard Goldstone. The report concluded that both sides committed war crimes during the conflict, which killed about 1,400 Palestinians and 13 Israelis.
Israel rejected the findings of that report. "We will not agree to a situation where the [Israeli Defense Forces] commanders and soldiers will be treated as war criminals after vigorously defending the citizens of Israel against a loathsome enemy," Israeli Prime Minister Benjamin Netanyahu said in October.
CNN was not able to receive a response from Hamas to the allegations in Sunday's report. According to some sources in Hamas, the organization has replied to all the questions during the initial Human Rights Watch investigation.
In February, Hamas released a summary of the steps it had taken to investigate wrongdoing, saying it had prevented militants from targeting civilians. At the time, the rights organization said that was "factually wrong," but said it was still reviewing a full Hamas report.
"Hamas can spin the story and deny the evidence, but hundreds of rockets rained down on civilian areas in Israel where no military institutions were located," said Joe Stork, deputy Middle East director for Human Rights Watch, in February. "Hamas leaders at the time indicated they were willing to harm civilians."
CNN's Kevin Flower contributed to this report.