MANILA, July 22 (Reuters) - U.S. Secretary of State Marco Rubio and his Chinese counterpart Wang Yi discussed Chinese President Xi Jinping's planned September visit to the United States on Wednesday on the sidelines of an Asian meeting, and the two ministers expressed concern about the Iran war and tensions in the South China Sea.

Rubio said he had extensive discussions with Wang about the need to lay the groundwork for a "very positive" visit by President Xi, and that their task was to manage the major differences between the two countries and ensure they did not get out of control.

The broader Association of Southeast Asian Nations (ASEAN) meeting in Manila comes amid escalating tensions between the United States and Iran, and at a time when tensions are rising between Beijing and the Philippines, a close U.S. ally, over an incident in the South China Sea on Monday that prompted both countries to recall their ambassadors.

During his meeting with the foreign ministers of the Association of ASEAN countries, who expressed their deep concern about the Middle East war, Rubio placed full responsibility for it on Iran.

He said, "The problem we face at the moment is that they do not seem serious about the talks... If they are serious, we will reciprocate. If they are not, we will do what is necessary to protect our interests, and the interests of our allies as well."

He stressed that Iran cannot be allowed to control the Strait of Hormuz, because that could set a dangerous precedent for other parts of the world.

* "A geopolitical weapon"

Rubio's remarks come in the wake of an opinion piece published by Philippine media on Tuesday, in which he criticized Beijing's behavior in the South China Sea, warning of "new and grave threats" if "those waters fall under the control of a power willing to use trade as a geopolitical weapon."

Beijing claims sovereignty over almost the entire South China Sea through a line on its maps that overlaps with the exclusive economic zones of Brunei, Indonesia, Malaysia, the Philippines and Vietnam, and this has sparked long-standing disputes over a large number of islands and maritime areas.

Australian Foreign Minister Penny Wang described a clash on Monday between the Chinese coast guard and Philippine navy personnel in the South China Sea as dangerous and destabilizing.

She added to reporters, "Countries in the region have a choice about how we all respond to this."

Chinese Foreign Ministry spokesman Lin Jian responded by saying that Australia has no right to interfere in the South China Sea and that Beijing "calls on the countries concerned to stop stirring up tension and inciting confrontation."

Disagreements between the Philippines and China have intensified in recent years, as Manila adopts a more hardline stance on the South China Sea, while simultaneously seeking to strengthen defense ties with the United States, as well as Australia and Japan.

Russian Foreign Minister Sergey Lavrov confirmed he will meet with Rubio in Manila on Thursday. Rubio said he will discuss the war in Ukraine with Lavrov, emphasizing that Washington is seeking to play a constructive role in ending the conflict.