The suitability of both Boris Johnson and Jeremy Corbyn to lead the UK's defences has come under attack during a pre-election debate.
Defence Secretary Ben Wallace, a Conservative, said Labour leader Mr Corbyn "does not know what side he's on".
Questions were also raised over Tory leader Mr Johnson's trustworthiness at the Royal United Services Institute event, which was attended by three of the major Britain-wide parties.
Speaking at the defence debate, Mr Wallace said increased defence spending by the Conservatives shows the party "knows what side it's on when it comes to security".
"A Government that recognises that the IRA, Hezbollah, Hamas, do not share our values, are not on our side and have spent many years killing our allies and indeed, killing us," Mr Wallace said.
"That is the thing I find the hardest about Jeremy Corbyn - I don't think he knows what side he's on and he wants to be the Prime Minister to defend this country."
However, Shadow Defence Secretary Nia Griffith defended Mr Corbyn, saying he is "not a pacifist" and would do "whatever it takes" to defend the UK.
"Jeremy Corbyn takes the defence and security of this country extremely seriously and will do whatever it takes to defend this country," Ms Griffith said.
"The point is, he is a very thoughtful leader who wants to see the full facts and wants to have the full information in any decision making that he makes.
"So, he will take a very measured approach and as would all experts in the field."
She added: "At the end of the day, if it is a threat to security - as I have said and he has repeated on many occasions - he will do whatever it takes, and that is an absolute commitment."
Mr Corbyn was also questioned by Labour peer and former head of the Royal Navy, Lord West.
He said he is "really, really worried" by Mr Corbyn's failure to clarify his position on the UK's nuclear deterrent, adding he would be "much happier" if Ms Griffith's finger was on the nuclear button.
She said: "The point is - is that when you are faced with the ultimate defence and security of your country then you may very well do things that perhaps you would not do in normal circumstances and therefore it will remain as a deterrent."
Labour committed to renewing the Trident programme in its manifesto, despite Mr Corbyn previously saying he would not authorise a nuclear strike.
Liberal Democrat peer and chair of the International Relations and Defence Committee, Baroness Smith, then intervened to say nuclear weapons are not a deterrent if a potential leader of the country, Mr Corbyn, will not use them.
Meanwhile, Mr Johnson was also criticised.
An audience member raised questions over the Tory leader's previous comments regarding Iran and nuclear weapons, China and the failure to publish the report on Russian interference.
Ms Griffith urged Mr Johnson to publish the Russian interference report, saying it is "extraordinarily stupid of him".
She also said she was concerned by "careless comments" made by Mr Johnson which has left Nazanin Zaghari-Ratcliffe in "a far worse position" as a prisoner in Iran.
Baroness Smith also said herself and the Liberal Democrats "do not trust Boris Johnson on security and defence of the realm".
Mr Wallace argued the Tory leader has always worked against Iran acquiring nuclear weapons.