U.S. Secretary of State Mike Pompeo said on Sunday that a rift between Qatar and its Arab Gulf neighbors had gone on for too long.
Saudi Arabia, the United Arab Emirates, Bahrain and non-Gulf Cooperation Council (GCC) member Egypt cut diplomatic, transport and trade ties with Qatar in June 2017, accusing it of supporting terrorism and their regional foe Shi'ite Muslim Iran - something Doha denies.
The United States, an ally of the six-nation Sunni Muslim GCC, sees the rift as a threat to efforts to contain Iran and has pushed for a united Gulf front.
"When we have a common challenge, disputes between countries with shared objectives are never helpful," he said at a press conference in the Qatari capital Doha.
"They never permit you to have as robust a response to common adversaries or common challenges as you might," he added.
Doha says the boycott aims to undermine its sovereignty.
"We're hoping that the unity of GCC will increase in the days and weeks and months ahead," Pompeo said, adding that Gulf unity was essential for a planned Middle East Strategic Alliance that would also include Jordan and Egypt.