Already an endangered species, blue curbside mailboxes have become the target of thieves in the southwest metro and across the Twin Cities metro area, according to authorities.

There have been at least four mailbox break-ins in the southwest metro, including one over the weekend outside the post office in Chaska on Pine Street, police said.

Someone broke off the box's large brass padlocks and made off with its contents, obviously creating a potential for identity theft for whoever deposited mail there between 3:30 p.m. Saturday and noon Sunday, according to police.

"We do have some leads" on who might be responsible, Police Lt. Chris George said Thursday, but no arrests have been made in the Chaska case.

Three similar mail thefts occurred in neighboring Chanhassen in the past week, police added.

In addition, "U.S. postal inspectors report that they are investigating similar crimes across the Twin Cities metro area," a statement from Chaska police said.

The statement added that the break-in on Pine Street likely involved "a large quantity of mail [being] stolen."

However, U.S. Postal Service spokesman John Friess has his doubts, pointing out Thursday that the amount of mail in that box over the weekend likely would not have been substantial.

Chaska police are cautioning anyone who may have dropped letters or parcels in the Pine Street box after midafternoon Saturday until midday Sunday to "please make the appropriate notifications to protect yourself" against identity theft.

The blue mailboxes have been a staple of the American landscape for generations. The Postal Service said it had nearly 400,000 curbside collection boxes in the country at the start of 2000, but there were fewer than 154,000 as of 2015 as their use continues to decline.