A ''mafia'' gambling chief had been engaged to kill him in exchange for a gambling concession across Bangkok, he said.
Khun Suthep moved last night from the five-star Intercontinental Bangkok to a tent in Lumpini Park at 2am when a ''good policeman'' relayed news of the kill contract.
He called on police to answer questions about a grenade blast this afternoon that injured 36 protesters and demanded that Prime Minister Yingluck Shinawatra respond.
In a televised speech from the Pathumwan rally stage, Khun Suthep showed a picture claiming that a cap found at the scene belonged to a police unit in the deep south Narathiwat province.
Khun Suthep challenged investigators to explain the blast and said he was waiting for answers from national police chief General Adul Saengsingkaew and Lieutenant General Kamronwit Thoopkrachang from the Metropolitan Police Bureau.
Evidence handed to police by protest investigators included three unassembled M16 rifles, four walkie-talkies and a cap bearing an ''attacking unit'' logo.
Khun Suthep said that from 10am tomorrow, he would continue his walks through Bangkok streets knowing he was a target.
He said he had made preparations for his death, and that the protest movement would meet the hospital costs of the 36 people - including one man from Phuket - wounded in today's grenade blast.
Khun Suthep urged protesters to keep fighting until the Shinawatra family had been forced from the country: ''Prime Minister, you are evil.''
There had been 27 incidents involving violence perpetrated during this week's non-violent protest, Khun Suthep said, and yet the police had not managed to solve a single one.