According to a document issued by Saudi Arabia’s customs directorate on Tuesday, the Salwa border gate had been shut permanently since Monday night.
The letter said Saudi officials ordered the closure.
The move comes as an ongoing diplomatic crisis nears eight months.
The gate was first closed two weeks after Saudi Arabia, the United Arab Emirates, Egypt and Bahrain cut diplomatic and trade ties with Qatar on June 5, accusing it of financing “terrorism” and maintaining too close a relationship with their regional rival, Iran. Doha denies the allegations.
The border was then reopened for two weeks in August for pilgrims who wished to perform the annual Hajj pilgrimage to pass through.
At the time, Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman Al Thani welcomed the move, but said it was a “politically motivated decision”.
Although officially well-received by Qatar, the move had sparked outrage from Qatari citizens on social media, who demanded the siege be lifted entirely.
The Arab quartet blocked direct air and land transport to and from Qatar and closed their airspace to all Qatar Airways flights after severing ties with Qatar.
Earlier this month, the annual regional summit of the six GCC countries was cut short, failing to resolve the ongoing crisis.
As part of the blockade, the Saudi-led group also asked all Qatari nationals to leave their countries, but Doha has not imposed similar restrictions on the four Arab nations.