The Labour leadership hopeful Emily Thornberry has accused Jeremy Corbyn’s advisers of trying to drop references to Palestinian rocket attacks against Israeli civilians from the party’s 2019 election manifesto.

The shadow foreign secretary said she was left “deeply disturbed” by the move which she saw as evidence that the Labour leader’s key lieutenants were happy to tolerate the deaths of Israeli citizens.

“Disgustingly, attacks on Israeli civilians were being deliberately dismissed in a way that would never have been tolerated of attacks on any civilians in any other country around the world,” Thornberry wrote in a comment piece for Jewish News.

She claimed “Jeremy’s office” dismissed her repeated complaints about the planned deletion. In an email exchange, it was suggested that the decision was “balanced considering the considerable imbalance in the conflict”.

The alleged comments were made at a time when Corbyn’s advisers were already fighting off hundreds of allegations of antisemitic incidents within the party. Thornberry will now face pressure to name the aides who made the alleged comments.

In an attempt to distance herself from the allegations of antisemitism which have swirled around the Corbyn leadership era, Thornberry said the party must now “get down on our hands and knees” and ask the Jewish community for forgiveness.

In the article, Thornberry said she believed Corbyn’s reaction at a later meeting indicated the Labour leader “knew nothing about the row”.

But while the suggested change was never adopted, she wrote: “The whole process left me deeply disturbed at the mentality of the advisers around Jeremy.”

Were she to become Labour leader, she continued, stamping out antisemitism would be her “most urgent and immediate priority”.

Thornberry said that, if elected, she would adopt recommendations made by the Jewish Board of Deputies, the Jewish Labour Movement and the equalities watchdog investigating allegations of antisemitism within the party.

“As a veteran of the bitter struggle inside the shadow cabinet to get us to endorse the IHRA (International Holocaust Remembrance Alliance) definition of antisemitism, and all its examples, I know how hard these fights can be,” she said.

“And we then need to get down on our hands and knees to the Jewish community and ask them for forgiveness and a fresh start.”

It has also emerged that prosecutors are considering whether to bring charges against five people as part of an investigation into alleged antisemitism by members of the Labour party.

Four people were arrested and two interviewed under caution last year as part of the inquiry. Investigators have passed five files of evidence to the Crown Prosecution Service.

The investigation was prompted by an internal Labour dossier detailing antisemitic messages on social media allegedly posted by party members, which was obtained by the radio station LBC in 2018.

Reports at the time suggested that the documents included details of 45 cases, including one which allegedly read: “We shall rid the Jews who are a cancer on us all.”

Cressida Dick, the Metropolitan police commissioner, told LBC on Wednesday: “It is for the CPS to decide. It is a very complex crime type, to be honest – there is a lot for them to look at and a lot for them to consider as to whether there is either sufficient evidence to charge and whether it is in the public interest so to do.”

The Labour party has previously welcomed the police investigation and said: “Antisemitism has no place in our society and we are committed to challenging and campaigning against it in all its forms.”

The party did not respond to a request for a statement on Thornberry’s claims.