PORTLAND, MAINE—The European Union will conduct a more extensive review of a proposal to ban lobsters imported from Canada and the U.S., after a scientific panel concluded Sweden raised valid points in its request to declare the American lobster an invasive species.

The opinion of the European Union’s Scientific Forum on Invasive Alien Species sets in motion a broader review that also will take into account the opinions of North American officials, who’ve criticized the proposal to ban American lobsters.

The international dispute started when Sweden announced it had found 32 American lobsters in the country’s waters earlier this year and that they pose a threat to native crustaceans.

Lobstermen in the U.S. and Canada, which together export $200 million (U.S.) worth of lobster to EU countries each year, had hoped to stop the proposal before it moved any further.

A spokesman for the European Union stressed that the scientific panel’s conclusion is considered preliminary. The full review won’t be completed until spring at the earliest.

The expanded review will include issues raised by scientists in the United States and Canada, and it’ll also consider economic impact and means of protecting native lobsters other than an outright ban, said Iris Petsa, EU spokesman for maritime affairs and fisheries.

How the American lobsters ended up in Swedish waters is unclear.

Sweden’s Agency for Marine and Water Management contends the country is right to be cautious about the appearance of a foreign species. The agency also says more research is needed into the impact of cross-breeding of American and European lobsters.

But Robert S. Steneck, a University of Maine scientist, contends American lobsters don’t pose a threat to European lobsters in part because winter ocean temperatures along the coasts of European countries are too warm for American lobsters to reproduce.