The Puerto Rican Veterans Memorial in Boston's South End has been vandalized during a weekend dedicated to honoring service members.

Authorities said they believe the vandals — who pushed over a stone pillar and threw the Puerto Rican flag to the ground — struck Saturday night. The city is investigating the incident, and Boston Public Works crews and Boston Parks and Recreation staff members are working on repairs.

Boston Commissioner of Veterans Services Robert Santiago said the vandalism hits hard, especially on this weekend.

"Any time is bad timing when a memorial is damaged or defaced, but being that this is Memorial Day weekend and tomorrow is Memorial Day, it adds an extra ounce of significance," he said. "Remember what Memorial Day is all about. It's about taking a moment to reflect and recognize and honor all of our service members who have given and paid the ultimate price for the freedoms that we have today."

But, Santiago added, Boston will still honor and recognize the Puerto Rican men and women who have served the country. A service is planned at the memorial Monday at 12 p.m.

The memorial was unveiled in 2013 and is the first in the nation to honor service members from Puerto Rico. Around 200,000 Puerto Ricans have served in the U.S. military since the island became part of the United States in 1898, according to the Department of Defense.

WGBH News' Meredith Nierman and Mary Blake contributed to this article.