Jeremy Corbyn suggested British support for Israel was a "major factor" in motivating the 7/7 London bombers, just days after the tragedy.
The Labour leader made the comment in a column in the far-left Morning Star newspaper, published only 13 days after the bombings killed 52 people and injured hundreds more.
He was writing in response to a Chatham House report that had suggested Britain’s support for American interventions in Afghanistan and Iraq had motivated the four suicide bombers to attack three London Underground trains and a double-decker bus.
The report, produced 10 days after the attacks, warned about Britain's participation in the invasion of Iraq.
Mr Corbyn wrote that Tony Blair’s government had been sent into a “flat spin” by the report but that it “merely echoed what has been a common analysis for years — that the behaviour of the US, with British support, in Afghanistan and Iraq was bound to have a consequence in the West."
Mr Corbyn then wrote: “It also holds that a widely held belief that the US and Britain are supportive of Israel, despite the plight of the Palestinian people, is a major factor influencing opinion all over the Middle East."
He continued: “If poverty and discrimination in Britain push people towards carrying out acts of madness, then think of the background to the daily bombings in Afghanistan, Iraq and Palestine.
"Last weekend, 90 Iraqis were killed when a petrol tanker was bombed. In Afghanistan, more bombs went off. Israel threatened to launch a ground offensive into Palestine."
Mr Corbyn wrote in his July 20 2005 column - unearthed by investigative reporter Iggy Ostanin - of the “total condemnation” of the terror attacks he had witnessed from the local mosques in his constituency of those who “feel the need to kill over 50 people of all walks of life guilty merely of travelling on public transport.”
But he criticised the argument that there was a need to bolster security laws such as the Prevention of Terrorism Act and to use control orders, writing that he had “more sympathy” with the views of the “Muslim parliament's Dr Gesloum Siddique. who questioned whether we need any more laws at all.”
In June 2017, Mr Corbyn claimed a link between “wars our government has supported or fought in other countries and terrorism here at home”, after the bombing of an Ariana Grande concert at the Manchester Arena killed 22 people.