Japan and the United States are considering the introduction of safeguard measures that would enable Washington to restrict imports of Japanese cars should they surge under the envisioned Trans-Pacific Partnership free trade pact, negotiation sources said Thursday.

While the United States seeks measures to protect its auto sector amid persistent concern over a possible sharp increase in the number of Japanese car imports, Tokyo and Washington are struggling to reach a compromise on criteria for implementing the safeguard measures, seen as an "emergency" action, the sources added.

The two countries are discussing motor vehicles, insurance and other nontariff measures in bilateral negotiations being held in parallel to TPP talks.