London (CNN) The family of a British teenager killed in a road accident involving the wife of a American diplomat in August 2019 has called for the UK government to block the extradition of Julian Assange to the US, unless Washington agrees to send Anne Sacoolas in the opposite direction.

Radd Seiger, lawyer and spokesman for the family of Harry Dunn, said the US has "launched the single greatest attack on the so-called special relationship between the countries in modern memory" by declining the UK's requests to extradite Sacoolas , who is accused of causing Dunn's death while driving on the wrong side of the road last August.

He said the UK should respond by rejecting any American requests for extradition, including that of Julian Assange -- the WikiLeaks founder whose extradition hearing begins on Monday.

Assange was arrested in April last year at the Ecuadorian Embassy on a US extradition warrant, and faces 18 charges in the US for his alleged role in encouraging, receiving and publishing national defense information.

"No one is above the law and no one must be allowed to evade justice if they manage to flee a country, whether diplomat or not," Seiger wrote in a statement.

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