Britain's policy towards Syria has been "stupid" and it should apologise for supporting rebels who are fighting to overthrow president Bashar al-Assad, and work with him to combat terrorism, the country's deputy foreign minister, Faisal Mekdad, has said. Mekdad told the Guardian that it was up to David Cameron to stop Britons coming to fight in Syria – an increasing preoccupation for UK authorities in recent months. "We regret that British people are coming here to be killed and to kill Syrians," he said. "But we believe it is the responsibility of the British government to stop such an onslaught."

Mekdad used an interview in his Damascus office to demonstrate his government's growing confidence that things are going its way amid signs western countries are re-thinking their policies towards the conflict, which has cost an estimated 170,000 lives since it began with largely peaceful protests in 2011. He singled out William Hague, the foreign secretary, for "bragging" about UK support for the anti-Assad opposition.

"The British government is extremist in its views on Syria and they are still thinking and dreaming that their agents, the Muslim Brotherhood and the other takfiris (violent jihadis) can make the change they want. Why should I be diplomatic if Hague and Cameron are not dealing with us diplomatically? We don't have to be. And developments have proven that we are correct and they are stupid. They have to admit that they have failed."

The minister praised British MPs for rejecting calls for punitive military action against Syria following the August 2013 chemical weapons attacks that killed about 1,300 people in opposition areas. The attacks were widely blamed on the Damascus government, though it has always denied responsibility.

"The British parliament was more advanced in its analysis than its government which wanted to commit another aggression against Syria after the one that destroyed Iraq," he said. "We had our views about Saddam Hussein but we were against the aggression by the Blair government, in collaboration with the Bush administration. And now you can see the results of their great achievements in Iraq and after attacking Libya where there is no government and terrorism is flourishing and being exported to neighbouring countries and to Europe.

"These are the great achievements of the British governments, of invading Iraq, of invading Libya, of planning to invade Syria. And these are the results of the so-called Arab spring that was supported by the west, (allowing) the Muslim Brotherhood to control the entire region.

Mekdad referred to recent BBC Newsnight revelations about a 2012 plan by the Ministry of Defence to train a 100,000-strong moderate rebel force to fight Assad's forces. "We knew that the UK was deeply involved in all the attacks and crimes that were committed in Syria," he said. "We are sure that there are more revelations which will show how deep was the involvement of the UK government."