British Foreign Secretary William Hague has called Syrian President Bashar al-Assad "delusional" and described him as a leader presiding over a "slaughter".
Hague on Sunday said that he would announce this week 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.
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.
In an interview with British newspaper The Sunday Times publicised on Saturday evening, Assad accused London of wanting to arm terrorists in Syria.
Assad accuses Britain of escalating conflict
"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.
Speaking to BBC television, Hague said of Assad: "This is a man presiding over this slaughter."
"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 [Assad's interview with The Sunday Times] will go down as one of the most delusional interviews that any national leader has given in modern times."
In Saturday's interview, Assad dismissed the suggestion that Britain could play a constructive role in resolving the conflict.
"We don't expect an arsonist to be a firefighter," he said.
Offering a message to "anyone who is talking about the Syrian people", Assad said, "only Syrian people can tell the president to stay or leave, come or go, no one else".
Lebanese-British reporter Hala Jaber, who also interviewed Assad in 2011, spoke this time to the president in Damascus.
She said he drove himself to the location, "a relatively modest building", and was told "that despite regular explosions, Assad insists on maintaining a normal lifestyle including — to his security chief’s dismay — driving to the office in the morning."
Jaber said Assad, who was softly spoken throughout the sit-down interview, adopted a conciliatory tone when discussing future negotiations.
"We are ready to negotiate with anyone, including militants who surrender their arms," he declared.
"We are not going to deal with terrorists who are determined to carry weapons, to terrorise people, to kill civilians, to attack public places or private enterprise and to destroy the country."