Syrian President Bashar al-Assad said the Royal Air Force (RAF) airstrikes in Syria will fail because they are "illegal" and detrimental to Britain's anti-terror campaign.

Interviewed by Britain's Sunday Times at his palace in Damascus last week, Assad said unless there is cooperation with troops on the ground, the aerial bombing campaign will not be able to succeed on its own.

"It has to be from the air, from the ground, to have cooperation with troops on the ground — the national troops — for the interference to be legal," the Syrian leader said. "So I would say they [British leaders] don't have the will and don't have the vision on how to defeat terrorism."

"[The campaign] will be harmful and illegal and it will support terrorism, as happened after the coalition started its operation a year or so [ago] because this is like a cancer,'' he stressed. "You cannot cut out part of the cancer. You have to extract it. This kind of operation is like cutting out part of the cancer. That will make it spread in the body faster."

On Thursday, Britain expanded its airstrikes against ISIS militants in Syria upon the request of French President Francois Hollande for the Western allies to do more to combat the extremist group. The move was prompted by the Nov. 13 terror attacks in Paris that left 130 dead. The Islamic State (ISIS) claimed responsibility for those attacks.

Britain's RAF has been bombing ISIS targets in Iraq since 2014. Wednesday's decision to expand the strikes to Syria came after a 10-hour debate by parliamentarians in the House of Commons.

The United States, France and Russia have been carrying out bombing campaigns against militants in Syria where a civil war erupted in 2011.

The Syrian leader also praised Russia, his nation's long time ally, saying its involvement in the conflict is legal because it came with Syria's permission.

"The Russians can see this clearly. They want to protect Syria, Iraq, the region — and even Europe. I am not exaggerating by saying they are protecting Europe today,'' he said.

The Syrian President further ridiculed Europe for allegedly producing terrorists, stating: "How many extremist cells now exist in Europe? How many extremists did you export from Europe to Syria? This is where the danger lies. The danger is in the incubator," Assad said

He also said of the West: "If they are ready — serious and genuine — to fight terrorism, we welcome any country of government, any political effort. In that regard we are not radical, we are pragmatic. Ultimately, we want to resolve the situation in Syria and prevent further bloodshed."

The civil war has killed at least 250,000 people. President Obama says Assad has killed tens of thousands of his own people in the conflict, according to the United Nations estimates.