DUBAI/MANILA: Four more oil tankers changed direction on the Red Sea after Iran-aligned Houthi forces in Yemen warned ships not to use the southern route, even as U.S. Secretary of State Marco Rubio said that Iran is not serious about peace talks. 

Pakistan, which has been helping to mediate, criticized the disruption to this second key energy route, where three tankers had already turned back earlier in the week. Both Rubio and Pakistan said they still support the idea of negotiations.

A day earlier, the Houthis warned that they could target Saudi oil shipments heading south toward the Bab el-Mandeb Strait, passing areas they control along the coast. This adds to Iran's near-total blockage of the Strait of Hormuz in the Middle East. This showed a new threat to global oil supplies as the conflict between the United States and Iran becomes more intense.

Oil prices increased to almost a six-week high on July 22. Brent crude rose by 2.45 percent to US$93.24 per barrel at 1323 GMT, after earlier reaching $95.47. In the United States, gasoline prices have gone back above $4 per gallon, which has affected President Donald Trump's popularity ahead of the midterm elections in November.

Trump said on social media that the United States would respond strongly if Iran attacked ships in the Strait of Hormuz. He said the U.S. could destroy key infrastructure in Iran, such as bridges or power plants, in response to such actions. In recent days, U.S. airstrikes have expanded from southern areas to western and central parts of Iran.

An official from Iran's health ministry said that 53 civilians have been killed and 592 injured this month. The United States has said it does not target civilians.

Iran's Army Commander-in-Chief, Major General Amir Hatami, said the country had strengthened its military because it expected its opponents to break agreements. Iranian media also reported that Hasan Qashqavi, a spokesperson for the parliamentary National Security and Foreign Policy Committee, said that Trump is in a complicated situation.

Large amounts of Saudi oil have been transported each day to the Red Sea port of Yanbu to avoid the Strait of Hormuz. If ships cannot pass through the Bab el-Mandeb Strait in the south of the Red Sea, they must use the northern route through the Suez Canal, which adds several weeks to the journey.

Iran has attacked important water desalination and energy facilities in Kuwait and said it has also targeted U.S. military assets there and in Bahrain and Jordan. Rubio said the United States will defend its interests and those of its allies.

He said that the main problem is that Iran is not serious about negotiations. He added that if Iran shows it is serious, the United States will also engage seriously, but if not, the U.S. will take necessary action to protect its own interests and those of its allies. He made these remarks during a meeting of Southeast Asian foreign ministers in Manila.

Mediators have proposed a plan for a 10-day ceasefire, according to a senior Iranian official who spoke to Reuters on Monday. Analysts said that the Houthis' new threat to shipping is likely a strategic move by Iran.

Mahmoud Shehrah, an associate fellow in the Middle East and North Africa Program at Chatham House in the United Kingdom, said that Iran is trying to gain an advantage for negotiations.

The proposal is meant to save a temporary ceasefire agreement signed by the United States and Iran in June. Iran's Interior Minister Eskandar Momeni visited Pakistan this week and asked the country to continue its role as a mediator. Pakistan said it would continue its efforts but stressed that shipping safety must be ensured.

Iran has said it will keep control over the Strait of Hormuz, which it secured during the conflict that began on February 28 when the United States and Israel launched attacks. Rubio said that allowing Iran to maintain such control would create a dangerous example for other regions, including Southeast Asia, where several countries have territorial disputes with China in the South China Sea.