Israel's offensive against Hamas in Gaza at the beginning of the year was a "proportional response" to attacks by the Islamist group, the Foreign Ministry said in a defense brief on Operation Cast Lead released Thursday.

"Israel's resort to force in the Gaza Operation was both a necessary and a proportionate response to Hamas' attacks," the ministry said Thursday in a statement on the brief, which was published ahead of two harsh United Nations reports on the conflict expected to be released soon.

"While the Israel Defense Forces continues to investigate specific incidents during the Operation, the Paper demonstrates that Israeli commanders and soldiers were guided by International Humanitarian Law, including the principles of distinction and proportionality."

The ministry said the brief, titled "The Operation in Gaza - Legal and Factual Aspects," also details the context of the campaign.

Click here to view the full 160-page report.

According to the statement, the brief gives previously unpublished details of multiple Israel Defense Forces investigations into allegations made by various groups of violations of the law during Operation Cast Lead, the code-name for the 3-week offensive.

The paper reveals that IDF investigative teams are currently examining approximately 100 complaints, including 13 criminal investigations opened so far. A draft of two UN reports is expected to be given to Israel around the end of August, before they are officially presented to the Human Rights Council in mid-September. The reports are expected to be highly critical of the extent of civilian casualties in the Hamas-ruled territory during the operation.

The ministry added: "The Paper also gives a detailed account of Israel's humanitarian efforts in the course of the operation, particularly in the face of Hamas attempts to launch attacks during humanitarian pauses to allow aid to reach civilians, hijack aid and assistance, and hide within and behind medical and international facilities."

The brief concludes that more than 12,000 rockets and mortars fired by Gaza militants between 2000 and 2008 forced Israel to act. It says Hamas was to blame for civilian casualties by deploying its fighters in neighborhoods and that Israeli forces destroyed buildings only to protect themselves.

The IDF says that a total of 1,166 Palestinians were killed in the operation, the majority of whom were militants; Palestinians, however, say that more than 1,400 were killed, including over 900 civilians.

A Jerusalem-based research organization, NGO Monitor, hailed the document on Thursday as a welcome change in the way the Israeli government counters "bias." The group said the brief was a document containing "evidence central to examining the facade of research methodology in more than 500 NGO statements during and after the recent Gaza conflict."

NGO monitor noted that Amnesty International and Human Rights Watch claimed to have no evidence of Hamas' alleged use of "human shields" in Gaza.

"In contrast, the report quotes Hamas operatives who acknowledged rocket fire from schools and describe incidents in which Hamas activists requested children to wheel carts laden with rockets, in case IDF forces noticed them," the group wrote.