Singapore's Agri-Food and Veterinary Authority (AVA) has found radioactive contaminants in four samples of vegetables imported from Japan, prompting the authority to suspend imports of fruits and vegetables from two more Japanese prefectures.

The authority has so far tested 161 samples of fresh produce such as seafood, fruits, vegetables and meat, and four of the samples imported on Wednesday were found to be contaminated, including mitsuba, nanohana, mizuna and perilla leaf, it said.

The AVA also announced on Thursday that it is suspending imports of fruits and vegetables from Chiba and Ehime prefectures of Japan.

The authority has been closely monitoring imports of food from Japan and has announced on late Wednesday the suspension of food imports from four prefectures affected by the radioactive leak, namely Fukushima, Ibaraki, Tochigi and Gunma.

All the affected shipments have been detained and will be disposed, AVA said.

Importers Japanese foods were also facing stricter checks by the authority, which has said it will continue to monitor imports of food from Japan closely, local broadcaster Channel NewsAsia reported.