TOKYO (Reuters) -- North Korea demanded that Japan halt sanctions it has imposed in reaction to Pyongyang's missile launches, threatening "stronger action" if Tokyo continues with the measures, Kyodo news agency said on Friday.

"Japan is translating its criticism against us into action," the agency quoted Song Il-ho, North Korea's ambassador in charge of diplomatic normalization talks with Japan, as telling reporters in Pyongyang.

"This may force us to take stronger physical actions," as a response, he said. Asked what the steps may be, he said, "I leave that to your imagination," Kyodo reported.

Japan banned a North Korean ferry from entering Japanese ports for six months as part of a package of initial sanctions following Pyongyang's launch of a series of missiles that landed in the Japan Sea on Wednesday.

The ferry, the only regular direct link between Japan and North Korea, is an important conduit for carrying money to the communist state.

Tokyo and Washington are pushing for a UN Security Council resolution on North Korea, and Tokyo has also said it is considering further unilateral sanctions, including limiting cash remittances.