British Foreign Secretary William Hague said Sunday that Syrian President Bashar al-Assad was "delusional" for failing to see that the bloodshed in his country was at his own hands.
Hague said that he would this week announce more assistance to the Syrian opposition in the form of non-lethal equipment and refused to rule out the possibility of arming them in the future.
In an interview with British newspaper The Sunday Times, Assad accused London of wanting to arm terrorists in his country.
Britain has been pushing to lift a ban on the sale of arms to Syria's rebels, but at a meeting last month European Union foreign ministers ruled that only "non-lethal" aid and "technical assistance" could be given to the opposition.
"How can we expect them to make the violence less while they want to send military supplies to the terrorists and don't try to ease the dialogue between the Syrians?" Assad said in a rare interview with Western media.
The United Nations estimates 70,000 people have been killed in the 23-month conflict.
Hague told BBC television: "This is a man presiding over this slaughter.
"And the message to him is we, Britain, are the people sending food and shelter and blankets to help people driven from their homes and families in his name.
"We are the people sending medical supplies to try to look after people injured and abused by the soldiers working for this man.
"Assad thinks and is told by his inner circle that all of this is an international conspiracy, not the actual rebellion and revolt of his own people.
"This will go down as one of the most delusional interviews that any national leader has given in modern times."
In the interview, Assad dismissed the suggestion that Britain could play a constructive role in resolving the conflict, saying: "We don't expect an arsonist to be a firefighter."
He added that London had long been out of contact with Damascus and lacked credibility in Syria due to its dealings in the Middle East.