"I have the government's assurance over the Sri Lankan issue," Karunanidhi said on ending his fast.
He was on an indefinite fast under the memorial of late C N Annadurai early Monday morning. His son M K Azhagiri was also observing a fast.
Earlier in the day, Prime Minister Dr. Manmohan Singh and Congress Party President Sonia Gandhi called Karunanidhi.
Dr. Singh assured Karunanidhi that his government is in touch with Colombo.onia Gandhi also called the Dravida Munnetra Kazhagam supremo from Murshidabad in West Bengal and expressed her concern about the plight of Tamil civilians in Sri Lanka.
The telephone calls to the ailing 84-year-old Karunanidhi came as DMK supporters launched road blockages in Chennai, Madurai, Trichy and Erode, besides other Tamil Nadu cities.
Public transport was disrupted and some DMK cadres hurled stones at buses.
Police deployment was in place to prevent a breakdown in law and order.
Karunanidhi had clarified that the priority was not to ban the Liberation Tigers of Tamil Eelam (LTTE), but to save the lives of thousands of Sri Lankan Tamils.
In a telegram to Dr. Singh, Sonia Gandhi, External Affairs Minister Pranab Mukherjee, Karunanidhi had urged the Indian Government to issue a warning to Colombo to halt the war in Lanka immediately.
He had also asked the UN and the international community to intervene in the matter.
Last week, National Security Adviser M.K Narayanan and Foreign Secretary Shivshankar Menon visited Sri Lanka and urged Sri Lankan President Mahinda Rajapaksa and his government to work towards declaring a truce in the closing chapter of a 25-year war in which nearly 6,500 civilians have lost their lives since February 2009.
The meeting between Rajapaksa and the Indian envoys took place even as the international community continues to demand that Sri Lanka stop its offensive and the LTTE surrender to avert rising civilian casualties.
India's move is seen as a swift reversal by its Congress party-led ruling coalition, which backs efforts to wipe out a group India lists as a terrorist organisation, but faces election pressure in Tamil Nadu to protect Tamil civilians. (ANI)