The protesters across from the large US embassy compound in Seoul waved signs saying "Do not join a war of aggression" as their leaders weigh a "contribution" to the waterway's security.
US President Donald Trump has pressured ally South Korea to help in the Middle East war, which has seen Iran take a stranglehold on the strait key to global oil supplies.
"We cannot send our young people into a sea of death!" chanted the protesters, who number…