Jeremy Corbyn has been forced to defend comments in which he appeared to compare the actions of Islamic State (IS) militants in Iraq with those of the US military during and after the 2003 invasion.
The favourite to win the Labour leadership made the comments in a June 2014 interview with Moscow-funded news channel Russia Today.
In a video clip of the interview which surfaced online, Mr Corbyn was asked what could help the Iraqi military regain control of areas seized by IS, also known as Isis.
The Islington North MP replied: "It requires a sense of unity among people in Iraq that want to stay part of Iraq and also an acceptance and an understanding why so many people in so many of the cities in the north have been prepared to accept the Isis forces.
"Yes they are brutal, yes some of what they have done is quite appalling, likewise what the Americans did in Fallujah and other places is appalling."
After his comments attracted sharp criticism, Mr Corbyn was forced to clarify his opposition to the militants.
His spokeswoman said: "Jeremy Corbyn believes the violent ideology of Isis is a vicious, repugnant force that has to be stopped - where Jeremy Corbyn talks about the need for a political solution and compromise he means not with Isis but against Isis, working across the region and beyond to choke off supplies that help fund and arm them and working with neighbouring states in the region to come to common solutions."
Meanwhile, Mr Corbyn said he was ready to challenge Labour over a so-called "purge" in which voters in the leadership election are being barred from casting a ballot supposedly because they support another party.
Mr Corbyn has said that if significant numbers are banned "unfairly" then the decision to reject them "must be looked at again and challenged".
Many voters who have recently joined Labour as registered supporters or as affiliate members are being told their votes will not count as the party works to root out potential infiltrators into the leadership race.
The contest has been marred by concerns over "entryism" from hard left individuals or Tory supporters who could seek to turn the outcome by signing up as registered supporters for £3 under new party rules.
Some fear that the rules, introduced by Ed Miliband, could see surprise frontrunner Mr Corbyn win the contest due to support from voters who have previously opposed Labour.
But many of those who appear to have been barred are complaining on social media that they voted Labour in the last election but are still having their votes blocked.
Speaking after a rally in Nottingham, Mr Corbyn revealed he was talking to Labour officials about the issue.
He said: "I know there are a number of people that it seems slightly odd have been not allowed but there is a process of looking again at many of these applications. I'm obviously in touch with the Labour party officials on this.
"The staff of the Labour party both in London and Newcastle have worked incredibly hard to try and deal with the massive number of applications.
"I hope these little glitches can be ironed out. But the vast majority of people that registered online or through text messaging have been accepted, are getting ballot papers and are getting a voting opportunity.
"Yes, if there are significant numbers rejected in apparently an unfair way, then of course that must be looked at again and challenged. But the issue really is let's be happy about getting 600,000 people taking part in an election."