A convoy of two dozen vehicles arranged by the International Committee of the Red Cross (ICRC) and the United Nations to transport the sick was barred from crossing the frontline, the state-run Daily News said.
"The Tiger terrorists... (are) holding all those patients captive as human shields," the Daily News said.
It said the convoy had been detained by "gun-carrying" fighters and that there had been "heated argument" with Red Cross and UN officials.
The patients from the Puthukkudiriruppu area in the district of Mullaittivu were to be handed over to the military and transferred to a hospital in Vavuniya, which lies in a government-controlled area in the north.
The Red Cross spokeswoman in Colombo, Sarasi Wijeratne, declined to comment on the newspaper report. UN officials and the Tigers were not immediately available for comment.
Sri Lanka ordered most aid workers out of the rebel-held Wanni region last September, saying it was for their own safety as fighting between the Liber