Jeremy Corbyn faced fresh criticism in the internal row over antisemitism on Saturday after it emerged he turned down an invitation from Labour’s sister party in Israel to visit the Yad Vashem Holocaust museum and will send a party official instead.

Labour sources confirmed he had said existing commitments made it impossible to go and he would send deputy leader Tom Watson or general secretary Iain McNicol in November.

Corbyn received a furious letter from Isaac Herzog, leader of the Israeli Labour party, in April, after former London mayor Ken Livingstone made some controversial remarks about Hitler and Zionism. Herzog said he was “appalled” by Livingstone’s assertion that when Hitler won his 1932 election, “his policy then was that Jews should be moved to Israel”. After suspending Livingstone from the party, Corbyn was invited by Herzog to Yad Vashem “to witness that the last time the Jews were forcibly transported it was not to Israel but to their deaths”.

Corbyn did not reply for several weeks, but officials confirmed to the Observer he had told Herzog his diary was too full and McNicol would go instead.

Joan Ryan MP, chair of Labour Friends of Israel, accused Corbyn of a failure of leadership which would fuel debate about his views on the Middle East.“I’m very disappointed Jeremy turned down the invitation to visit Israel from our sister party. Given the deep concerns about his commitment to a two-state solution, his labelling of terror groups such as Hamas and Hezbollah as ‘friends’, and the allegations of antisemitism which have occurred on his watch, such a visit should have been a priority,” Ryan said.

Ken Livingstone, the former London mayor was suspended from the Labour party in April after comments he made on Hitler and Zionism Photograph: i-Images

Wes Streeting, the Labour MP for Ilford North, was also critical, saying: “It is not surprising that Jeremy Corbyn is not viewed as a potential prime minister by the public when he cannot handle diplomatic issues like this. This shows why so many people think he is not fit to be prime minister and why many Labour voters would prefer Theresa May.”

In June, Shami Chakrabarti, chair of Labour’s antisemitism inquiry set up by Corbyn after the Livingstone episode, concluded the party was not overrun by antisemitism. There were further party tensions when Chakrabarti was recommended by Corbyn for a peerage.