(Corrects spelling in headline, 2nd summary point, paragraphs 1, 3)
By Hyun Young Yi
SEOUL (Reuters) -South Korea's impeached President Yoon Suk Yeol has sent a letter rallying his supporters saying he would "fight until the end" as he faces an attempt by authorities to arrest him over his short-lived Dec. 3 martial law, a lawyer said on Thursday.
"I am watching on YouTube live all the hard work you are doing," Yoon wrote in the letter late on Wednesday to the estimated hundreds of supporters who have gathered near his official residence protesting his investigation.