"It is an ambitious target, but I will see that all the internally displaced people are given land to build homes," the president said in an interview to AFP. "I am setting up a mechanism to complete this process within six months."
Sirisena, elected last January, has won praise for starting to hand back land after the end of one of South Asia's longest and bloodiest ethnic wars, pitting the government against Tamil separatists.
The president said he would give land to civilians displaced by war in the embattled northern and eastern provinces, and also the northwestern coastal region of Puttalam, by the middle of this year.
During a visit to Jaffna in the north last month, where much of the fighting took place, Sirisena said he visited a refugee camp which has been home to about 1,300 families for the past 25 years.
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"This is an unacceptable situation. I want to end this problem once and for all," he said. "For many people the main issue was lack of land and that is something we will resolve in the next six months."
He said he would travel to Jaffna this month to formally hand over about 700 acres of land as part of the plan and in line with an election promise he had made.
Sirisena, 64, came to power with the backing of Sri Lanka's minority Tamils and Muslims in addition to the majority Sinhalese on the back of promises to ensure ethnic reconciliation and end the corruption and nepotism of his predecessor.
He said the government was also working on a mechanism to investigate allegations of war crimes in the final stages of the conflict.
The president said he would also call for proposals for a new constitution to ensure the country did not slip back into war.
"We can't rush the accountability process," Sirisena said. "Some people want it to be like instant noodles. We can't do that. We have to be responsible and respect rule of law.