Jerusalem (PTI): Israel had started preparations for the largest military offensive on Gaza six months back, a media report said here on Sunday, contradicting official claims that the operation was forced by Hamas' rocket attacks against the Jewish state and its refusal to renew the ceasefire.

"Long-term preparation, careful gathering of information, secret discussions, operational deception and misleading of the public - all these stood behind the Israel Defense Forces (IDF) "Cast Lead" operation against Hamas targets in Gaza Strip, which began on Saturday morning," daily Ha'aretz said.

The disinformation effort took Hamas by surprise and served to significantly increase the number of its casualties in the strike, defence officials reportedly told the daily.

Sources in the defence establishment said that Defense Minister Ehud Barak instructed the IDF to prepare for the operation over six months ago, even as Israel was beginning to negotiate a ceasefire agreement with Hamas, it said.

Barak then was of the view that although the lull would allow Hamas to gear up for a showdown with Israel, the Israeli army also needed time to prepare, the sources said.

The Israeli defence minister gave orders to carry out a comprehensive intelligence-gathering drive which sought to map out Hamas' security infrastructure, alongwith that of other militant organisations operating in the Strip.

The Israeli army in a press statement on Saturday claimed that the operation extensively targeted Hamas installations based on extensive intelligence gathering.

The plan of action implemented in 'Operation Cast Lead' was only a 'blueprint' until a month ago. However, following dozens of rocket attacks on Israel on Nov 19, it was brought for the final approval of Barak, who met Premier Ehud Olmert last week to finally approve the operation.