Cornwall Island is entirely on the Canadian side of the border but south of the new border post, which is at the north end of the Seaway International Bridge. (Google Maps)

An international border crossing at a Cornwall, Ont., bridge between Canada and the United States was shut down for about five hours Saturday afternoon amid ongoing tensions between the Canada Border Services Agency and area Mohawks.

Cornwall police were called to the bridge around 12:30 p.m. ET and began diverting traffic from the area. The unexplained closure lasted until about 5:30 p.m. ET.

The Cornwall border post was previously on Cornwall Island in Akwesasne Mohawk Territory, which spans the Canada-U.S. border and includes the island.

Cornwall police redirected traffic away from the border crossing for about five hours on Saturday. (CBC)However, that post was shut down June 1 by the border agency after Mohawks protested the decision to arm border guards.

The international crossing remained closed from that date until July 13, when a temporary border post was opened at the north end of the Seaway International Bridge.

Cornwall Island is entirely on the Canadian side of the border, but south of the new border post, so people passing between Cornwall and Cornwall Island are now required to stop at the new post, even though they never leave Canada.

Mohawks travelling in their territory between New York and Cornwall Island, including those who live on the island but work in the United States, are also required to go to the border post in Cornwall.

On Friday, the Mohawk Council of Akwesasne accused the CBSA of seizing vehicles belonging to Mohawk residents who don't report to the new border post — and demanding $1,000 to recover them.

Under the Immigration and Refugee Protection Act and the Customs Act, the CBSA "is required to ensure that all travellers to Canada report to the temporary port of entry located in Cornwall," agency spokesperson Tracie LeBlanc said in an email statement Saturday.

"These rules apply equally to all travellers."

LeBlanc said that "since July 13, we have been clearly and consistently communicating the legal obligation for travellers to Canada to report directly to the port of Cornwall."

With files from The Canadian Press