Greenpeace occupied Shell oil rig heading to arctic drill site

It is likely that the statement concerning not attempting to physically stop the ship is to pre-empt the US from choosing to act as Russia did when Greenpeace boarded one of their drilling facilities. Russia chose to send paramiltary attack teams and charge unarmed Greenpeace activists with piracy. It took a major international mobilization of naming and shaming Russia to force Putin to abandon those charges.