By Brian Ellsworth MIAMI (Reuters) -Antigua and Barbuda is willing to help Britain seize yachts owned by sanctioned Russian oligarch Roman Abramovich, the Caribbean nation said on Friday, adding London must seek such assistance via an international treaty. The Financial Times first reported the vessels Halo and Garcon, currently moored in Antigua and Barbuda, were owned by Abramovich via a British Virgin Islands company that was on the Britain’s sanctions list. Antigua alone would have no way to seize or detain the vessels because they have not been linked to any crimes committed there, said R…