US State Department said Wednesday that closer ties between Iran and Syria should be of great concern, not just to US allies and the region, but to the world more broadly.

Department spokesperson, Vedant Patel, told reporters Washington has made clear to partners that it does not support others normalizing ties with Damascus.

Iranian President Ebrahim Raisi met his Syrian counterpart Bashar al-Assad in Damascus on Wednesday in the first visit by an Iranian head of state since Syria's war began in 2011, underlining close ties as Syrian relations with Arab states thaw.

Speaking to pro-Iran broadcaster al-Mayadeen on the eve of his visit, Raisi said the trip would "consolidate and develop" ties with Syria and other allies, including Lebanese armed group Hezbollah, which also intervened in Syria on Assad's behalf.

Raisi's visit comes as Iran and regional rival Saudi Arabia rebuild relations after years of tensions, and as Arab states that shunned Assad - including Riyadh - rebuild ties with his government.

Assad, speaking alongside Raisi, welcomed "the development" of ties between Tehran and Riyadh.

Raisi and Assad signed a long-term strategic cooperation agreement, including a memorandum of understanding on oil industry cooperation, the Syrian state news agency reported.

Raisi praised Syria for resisting what he described as U.S. pressure and confronting "takfiris", a term used to describe jihadists such as Islamic State. "Iran will always stand by Syria ... and supports its sovereignty," he said.

Raisi and Assad signed a long-term strategic cooperation agreement, including a memorandum of understanding on oil industry cooperation, the Syrian state news agency reported.

Reporting by Reuters