By Michael Martina and Nestor CorralesMANILA, July 22 (Reuters) - U.S. Secretary of State Marco Rubio will meet Chinese Foreign Minister Wang Yi on Wednesday during aregional gathering led by the Southeast Asian bloc ASEAN, where top diplomats voiced concern about renewed Middle East hostilities and tension in the South China Sea.The two are expected to discuss a possible U.S. summit between their leaders flagged for the end of September by President Donald Trump, with Rubio saying on Sunday it was still anticipated.Their meeting comes amid a fragile truce between the world's biggest economies that could be complicated by President Donald Trump's accusations of Chinese meddling in U.S. elections, which Beijing has denied.The broader ASEAN meeting in Manila comes amid a flare-up in the conflict between the United States and Iran, while tension simmers between Beijing and close U.S. ally the Philippines over an incident in the South China Sea that led each to summon the other's ambassador.Meeting with foreign ministers of the Association of Southeast Asian Nations, who expressed serious concern about the Middle East war, Rubio put the blame squarely on Iran."The problem we're having right now is that they're not serious about talks," he said. "If they're serious, we're serious. If they're not, then we will do what's necessary to protect our interests, and also the interests of our allies."Rubio stressed that Iran could not be allowed to control the Strait of Hormuz, as it could set a dangerous precedent for other parts of the world, including Southeast Asia.'COMMERCE AS A GEOPOLITICAL WEAPON'His remarks follow an opinion piece in Philippine media published on his arrival in Manila on Tuesday that took aim at Beijing, in which he said ASEAN countries were confronting "new and coercive threats" in the South China Sea."If those waters fall under the control of a power willing to use commerce as a geopolitical weapon, both the United States and the ASEAN states would face dire new threats to their sovereignty, security, and economic futures," Rubio wrote.Beijing claims sovereignty over almost the entire South China Sea via a line on its maps that cuts into the exclusive economic zones of Brunei, Indonesia, Malaysia, the Philippines, and Vietnam, and is at the centre of long-running disputes over a multitude of islands and features.Australia's Foreign Minister Penny Wong said Monday's altercation between China's coast guard and Philippine navy personnel in the South China Sea prompted real concern about "destabilising and risky" behaviour."The countries of the region have a choice to make about how we all respond to that," Wong told reporters on the sidelines of the meeting, adding that the Middle East conflict could deteriorate further, without much warning.The event is also being attended by Britain, Canada, the European Union, India, Japan, Russia and South Korea.CHINA, ASEAN CAN BE ANCHOR FOR REGIONAL PEACE, WANG SAYSRows between the Philippines and China have increased in recent years as Manila takes a bolder stance on the South China Sea, while pursuing closer defence ties with the United States, Australia and Japan.In talks with ASEAN's secretary-general on Tuesday, Wang said some elements of the Philippines' security apparatus had engaged in deliberate provocations that served interests of "external forces", and Beijing was willing to work with ASEAN to "eliminate interfering factors".Wang met ASEAN counterparts on Wednesday and said mutual trust, openness and inclusiveness were key to their prosperity and a foundation to "get things done"."Let us be the anchor for regional and global peace and development," he said.Rubio also joined counterparts from India, Australia and Japan for a meeting of the Quad grouping that Beijing has criticised as being Cold War-like and aimed at containing China's development.In a joint statement they reaffirmed commitment to "strengthening a free and open Indo-Pacific and our unwavering support for ASEAN unity and centrality". (Reporting by Michael Martina, Karen Lema, Nestor Corrales, Mikhail Flores; Additional reporting by Liz Lee in Beijing; Writing by Martin Petty; Editing by Christian Schmollinger and Clarence Fernandez)