Updated 0445 GMT
The Canadian Tamil MP, Rathika Sitsabaiesan, who recently arrived in the North-East, is under house arrest, reported TamilNet.
According to the news site, around 8-10 officers from Sri Lanka's Terrorism Investigation Department arrived at the hotel that Ms Sitasabaiesan was staying in Jaffna, on Tuesday night.
Colombo Gazette also cited "Jaffna media reports" as stating no one was allowed to meet the Canadian MP at her hotel.
Minister of State for Foreign Affairs Lynne Yelich also tweeted that she was "concerned" about the reports and the Canadian High Comissioner in Colombo would be investigating the case further. She added that Sri Lanka stated no official arrest warrant was issued for Ms Sitsabaiesan.
Arriving on Saturday, Ms Sitsabaiesan had visited the militarised zone in Valikaamam North and the Sababathipillai ICP camp, before meeting informally with the Provincial Councillor Ananthi Sasitharan, and the TNA MP Sreetharan in Kilinochchi.