The US Senate on Wednesday rejected a resolution aimed at curbing President Donald Trump's authority to continue military strikes on Iran, in a narrow congressional show of support for a conflict launched without explicit approval from lawmakers.

The bipartisan measure, introduced by Democrat Tim Kaine and Republican Rand Paul, would have required the withdrawal of US forces from hostilities against Iran unless Congress authorizes the campaign.

BEIJING, March 4 (Reuters) - China will send a special envoy to the Middle East for mediation,Foreign Minister Wang Yi told his Saudi Arabian and UAE counterparts on Wednesday according to statements from his ministry, as conflict in the region continued to escalate.

China appreciates Saudi Arabia's restraint and insistence on resolving differences through peaceful means, Wang was quoted as saying in a phone call with the Saudi minister by the Chinese ministry.

By Parisa Hafezi and Angus McDowall

DUBAI, March 4 (Reuters) - Iran’s Revolutionary Guards have tightened their grip on wartime decision‑making despite the loss of top commanders, senior sources say, driving a hardline strategy that is propelling Tehran's drone‑and‑missile campaign across the region.

By Idrees Ali, Phil Stewart, Doina Chiacu and Susan Heavey

WASHINGTON, March 4 (Reuters) - Iran is firing fewer missiles than it did at the start of the war on Saturday, the top U.S. general said on Wednesday, as he argued Iran's military capabilities were greatly diminished as the United States expands its strikes inside Iran.

"We will now begin to expand inland striking progressively deeper into Iranian territory, and creating additional freedom of maneuver for US forces," General Dan Caine, chairman of the Joint Chiefs of Staff, told a news briefing at the Pentagon.

March 4 (Reuters) - At least 80 were people killed in a U.S. submarine strike on an Iranian warship in the Indian Ocean, Sri Lanka's deputy foreign minister told local television on Wednesday.

(Reporting by Uditha Jayasinghe, writing by Shilpa Jamkhandikar; Editing by YP Rajesh)

By Yousef Saba, Jonathan Saul and Anna Hirtenstein

March 4 (Reuters) - The U.S.–Iran war widened on Wednesday after a U.S. strike hit an Iranian warship off Sri Lanka, deepening a crisis that has paralysed shipping through the Strait of Hormuz for a fifth day and choked off vital Middle East oil and gas flows.

The U.S. submarine strike on the Iranian vessel came as U.S. President Donald Trump pledged to provide insurance and navy escorts to ships exporting oil and gas from the Middle East in a bid to contain soaring energy prices.

WASHINGTON, March 4 (Reuters) - The U.S. military said on Wednesday that it killed an Iranian official who headed a unit behind an alleged assassination plot against President Donald Trump.

"The leader of the unit who attempted to assassinate President Trump has been hunted down and killed. Iran tried to kill President Trump and President Trump got the last laugh," Defense Secretary Pete Hegseth told a news briefing.

Hegseth did not name the individual but said the operation took place on Tuesday.

March 4 (Reuters) - Ayatollah Ali Khamenei's son Mojtaba has emerged as frontrunner to succeed his late father as Iran's supreme leader after years spent forging close ties with the elite Revolutionary Guards and building influence in the clerical establishment.

Mojtaba Khamenei, 56, has survived the U.S.-Israeli air war on Iran and is seen by Iran's establishment as a potential successor to his father, who was killed in an airstrike on Saturday, two Iranian sources said on Wednesday.

More relieved passengers arrived home from the Gulf region on Wednesday as further flights resumed five days into the war triggered by US-Israeli attacks on Iran.

Aviation analytics company Cirium said that of the more than 36,000 flights scheduled to fly to or from the Middle East, more than 20,000 had been cancelled since Saturday.

As airlines resumed limited flights out of hubs including Dubai and Riyadh, governments also chartered planes to bring home citizens affected by the turmoil, which stranded tens of thousands of travellers worldwide.

WASHINGTON, March 4 (Reuters) - U.S. Defense Secretary Pete Hegseth said on Wednesday the United States was winning in the war against Iran and that the U.S. military could fight as long as needed.

"Our air defenses and that of our allies have plenty of runway. We can sustain this fight easily for as long as we need to," Hegseth said.

(Reporting by Idrees Ali, Phil Stewart, Doina Chiacu and Michelle Nichols; Editing by Andrew Heavens)