Philip Hammond, the foreign secretary, has bluntly rejected calls for Britain to enlist Syria's president, Bashar al-Assad, as an ally in the fight against Islamic State (Isis) extremists.

In an interview on the BBC's World at One, he said the idea, floated by one of his Conservative predecessors as foreign secretary, Sir Malcolm Rifkind, had no attraction to the government at all.

"We may very well find that we are fighting, on some occasions, the same people that [Assad] is but that doesn't make us his ally," Hammond said. "It would not be practical, sensible or helpful to even think about going down that route."

Rifkind had told the programme that it was important for the west to be realistic. Even though the US and the UK came close to launching air strikes against the Assad regime last summer, there could be a case for collaborating with Assad in some way to ensure the defeat of Isis, Rifkind suggested.

"I think we have to be harshly realistic, which means we don't pretend we are chums of the Syrian regime – they are a ghastly regime, they are a horrid regime – but just as during the second world war Churchill and Roosevelt swallowed hard and dealt with Stalin, with the Soviet Union, not because they had any naivety about what Stalin represented but because that was necessary in order to defeat Hitler, and history judged them right in coming to that difficult but necessary judgment," Rifkind said.

Richard Dannatt, the former head of the army and at one time a defence adviser to the Conservatives, made the same argument in an interview on the Today programme on Friday morning.

But Hammond argued that Rifkind and Lord Dannatt were both wrong.

"I do not think that engaging in a dialogue with the Assad regime would advance the cause that we are all advocating here," Hammond said.

"General Dannatt I heard talking about the adage that my enemy's enemy is my friend. I have said very often that one of the first things you learn in the Middle East is that my enemy's enemy is not necessarily my friend.

"We may very well find that we are aligned against a common enemy. But that does not make us able to trust them, it does not make us able to work with them and it would poison what we are trying to achieve in separating moderate Sunni opinion from the poisonous ideology of Isil [Islamic State] if we were to align ourselves with President Assad."

Dannatt argued that one reason for talking to Assad would be to ensure that, if the US or the UK wanted to launch air strikes against Isis bases in Syria, they were not targeted by Syrian air defences.

But Hammond dismissed this idea. "I don't know where the idea comes from that Assad has to assent to a military intervention in his country. There's a civil war raging," he said.

Hammond insisted that the government was committed to fighting Isis as part of an international coalition and that this involved taking action on the security front, the political front and the humanitarian front.

Britain would not provide ground troops, he insisted.

"This needs to be a fight that is dealt with by Iraqis on the ground. Of course we can provide them with technical support, material, weapons, ammunition, intelligence, training, and the United States is providing them with an element of combat air cover. All of those things can be helpful.

"Putting western boots on the ground to fight would not only be something that we would be very unlikely to get consent for from the British public, but something that would simply not be helpful, and has not been asked for."

Hammond did not rule out Britain supporting the US in launching air strikes against Isis – a move proposed by Dannatt in his Today interview – although government sources have played down the prospect of this happening.

But Hammond did confirm that Britain was looking "sympathetically" at calls to provide arms to Kurdish peshmerga fighters who are at war with Isis, and he said Britain would also consider supplying arms to the Iraqi government for the same reason once an inclusive, representative government was in place.

He also said the government would consider supplying arms to the moderate opposition in Syria. Until now, only non-lethal aid has been supplied, he said.

"It is something that we will want to continue to review. As the situation on the ground changes, we will want to look periodically at the situation and make a decision as to what is in Britain's best national interest," he said.