In the letter, published by the Royal Hashemite Court on its official Facebook page on Monday, Hamzah, King Abdullah II's half-brother, said: "I place myself in the hands of His Majesty," Xinhua news agency.
Hamzah said he will remain loyal to the King and supportive of the King and Crown Prince Hussein, and also continue to honour the legacy of the Hashemite family, according to the letter.
Prince Hamzah said the national interests of Jordan are above all considerations and that everyone should stand behind the King in supporting the country and the national interests.
On Sunday, Foreign Minister Ayman al-Safadi said investigations showed there were movements by Hamzah, Awadallah and Sharif Hassan Ben Zeid targeting the Kingdom's stability and security, and that they were in contact with "foreign parties."
As part of a thorough security operation and investigation, Awadallah and Sharif Hassan, along with around 15 other persons, were arrested the previous day for involvement in a plot, according to Safadi.
In a related development also on Monday, authorities confirmed that King Abdullah II has entrusted Prince Hamzah's issue to his uncle Prince Hassan, and decided that it would be handled as a family matter.
Hamzah, 41, was Jordan's Crown Prince between 1999 and 2004.
At the time, he said he will remain a devout support to Abdullah in official letter published by state media.