"I received your letter in which you wrote with detail and analysis about the recent Palestinian jihad. Your struggle is the resistance against oppression, heresy and arrogance," the Leader wrote in his letter to Hamas political bureau chief Ismail Haniyeh.
"Such a struggle pleases the Almighty, Revered God and is the proof of 'O you who have faith! If you help Allah, He will help you and make your feet steady'," the Leader wrote, citing verse 7 of the 47th chapter of the Holy Qur'an.
"You will be victorious by the power of God and cleanse the holy land from the filth of the usurpers, God willing," Ayatollah Khamenei added.
In a separate letter to Islamic Jihad Secretary General Ziad al-Nakhala, Ayatollah Khamenei predicted that the "final victory" will come to the Palestinians.
"I received your brotherly letter. The great and victorious jihad of you Palestinian brothers lit up the eyes of your lovers all over the world," the Leader wrote.
"Our hearts are with you at the scene of your struggles and our prayers for the continuation of your victories are constant," he said.
"The divine promise is true when he said: 'Allah will surely help those who help Him', and you will see the ultimate victory, God willing," Ayatollah Khamenei said, referring to verse 40 of the 22nd chapter of the Qur'an.
On Sunday, Nakhala had sent a letter of thanks to the Leader following the victory of the Palestinian resistance.
"Your continued support at all levels played the greatest and most prominent role in what the Palestinian people achieved in the battle of Saif al-Quds (Operation al-Quds Sword)," he wrote in the letter.
"Through Your Eminence, I thank our brothers in the Quds Force who have been with us for many years and provided us with everything they have experienced," Nakhala said.
The secretary general of the Palestinian Islamic Jihad also paid tribute to the memory of Iran's legendary commander General Qassem Soleimani who was assassinated in a US drone strike in Baghdad in January 2020.
"The companions of Martyr Soleimani and his brothers Haj Qa'ani and his assistants were present with us in the management of this battle every single moment, and their presence was blessed and had by many benefits," he said, referring to Quds Force chief General Ismail Qa'ani.
"On behalf of myself and my brothers in the central command of the Islamic Jihad movement and its members, as well as the command of the al-Quds Brigades and its fighters, I congratulate you," Nakhala added.
Haniyeh had also written to the Leader and on Friday, he thanked Iran in his first speech after Israel submitted to a ceasefire.
"We thank the Islamic Republic of Iran, which did not withhold any financial assistance or weapons from the resistance," he said.