"Our leader Velupillai Prabhakaran has told Mr Patten that it is not at all in the hands of the Liberation Tigers to ensure that there is no return to violence," Tiger political wing leader SP Thamilselvan was quoted as saying by the pro-rebel website, tamilnet.com.
He said Prabhakaran had made it clear to Patten that the Tigers remained committed to resolving the conflict peacefully.
"It is completely up to the Sinhala polity to see there is no return to war," he told reporters in the rebel-held town of Kilinochchi shortly after Patten's talks there with Prabhakaran.
Patten had faced noisy protests from the majority Sinhalese before he left for Killinochi in the rebel-controlled northern part of Sri Lanka for talks with the separatist leader.
Members of the Sinhalese hard-line Patriotic National Movement (PNM) were protesting against the EU leader's meeting with Prabhakaran.
The PNM draws support from key members of President Chandrika Kumaratunga's People's Alliance.
However, Patten, who had talks with Kumaratunga in Colombo on Tuesday, said that no one he met with had objected to his meeting with Prabhakaran.
Earlier this month, the Liberation Tigers of Tamil Eelam (LTTE) supremo had received Norway's deputy Foreign Minister Vidar Helgesen and also had talks with several other visiting dignitaries, including Japan's special peace envoy Yasushi Akashi.
"He should make it clear that he has given up violence for good and has settled for politics and the ballot box"
EU External Relations Commissioner
Patten said he would be seeking assurances from Prabhakaran that he was committed to implementing the Norwegian-brokered ceasefire declared in February last year between government troops and the Tigers.
"He should make it clear that he has given up violence for good and has settled for politics and the ballot box," Patten told the BBC before leaving for Kilinochchi.
Patten was also critical of the LTTE's practice of recruiting child soldiers and sending some of them as suicide bombers to carry out attacks and political assassinations.
The EU commissioner's visit follows a political stand-off between the President and Prime Minister Ranil Wickremesinghe which nearly derailed efforts to end the Tamil Tigers' decades-long violent uprising in support of an ethnic homeland.
The PNM is also staunchly opposed to Norway's bid to broker peace between the Colombo government and the Tigers. The European Union is a key supporter of Oslo's peace attempts.