Tens of thousands of people marched in Baghdad on Saturday to mourn Iran's military commander Qasem Soleimani and Iraqi militia commander Abu Mahdi al-Muhandis, who were killed in a US air strike that has raised the specter of wider conflict in the Middle East.Friday's attack, authorized by President Donald Trump, signaled a major escalation in a Middle East "shadow war" between Iran and the United States and American allies, mainly Israel and Saudi Arabia. Gholamali Abuhamzeh, a senior commander of Iran's elite Revolutionary Guards, said Tehran would punish Americans "wherever they are in reach," and raised the prospect of possible attacks on ships in the Gulf.The US Embassy in Baghdad urged American citizens to leave Iraq following the strike at Baghdad airport that killed Soleimani. Dozens of American employees of foreign oil companies left the southern Iraqi city of Basra on Friday.Close US ally Britain warned its nationals on Saturday to avoid all travel to Iraq, outside the autonomous Kurdistan region, and avoid all but essential travel to Iran.Soleimani, a 62-year-old general, was Tehran's most prominent military commander and - as head of the Quds Force, the foreign arm of the Revolutionary Guards - the architect of Iran's spreading influence in the Middle East.Muhandis was the deputy commander of Iraq's Popular Mobilisation Forces (PMF) umbrella body of paramilitary groups.An elaborate, PMF-organized procession to mourn Soleimani, Muhandis and other Iraqis killed in the US strike began in Baghdad's heavily fortified Green Zone.The marchers included many militiamen in uniform for whom Muhandis and Soleimani were inspirational heroes. They waved Iraqi and militia flags. They also carried portraits of both men and plastered them on walls and armored personnel carriers in the procession.They chanted, "No No Israel" and "No No America."Prime Minister Adel Abdul Mahdi and Iraqi militia commander Hadi al-Amiri, a close Iran ally and the top candidate to succeed Muhandis, attended.The procession was due to proceed by car to the Shi'ite holy city of Kerbala and end in Najaf, another sacred Shi'ite city where Muhandis and others will be laid to rest.The US strike followed a sharp increase in US-Iranian hostilities in Iraq since last week when pro-Iranian militia attacked the US Embassy in Baghdad following a deadly US air raid on the Kataib Hezbollah militia, founded by Muhandis.A senior Trump administration official said Soleimani had been planning imminent attacks on US personnel across the Middle East. Democratic critics of the Republican president said Trump's order was reckless and that he had raised the risk of more violence in a dangerous region.Soleimani's body will be transferred on Saturday to the southwestern Iranian province of Khuzestan that borders Iraq. Then on Sunday it will be taken to the Shi'ite holy city of Mashhad in the northeast and from there to Tehran and on to his hometown Kerman in the southeast for burial on Tuesday, Iranian state media reported.'VITAL AMERICAN TARGETS'On Friday, Iranian Supreme Leader Ayatollah Ali Khamenei vowed harsh vengeance against the "criminals" who killed Soleimani and said his death would intensify the Islamic Republic's resistance to the United States and Israel.Abuhamzeh, the Revolutionary Guards commander in Kerman province, mentioned a series of possible targets for reprisals including the Gulf waterway through which a significant proportion of shipborne oil is exported to global markets.“The Strait of Hormuz is a vital point for the West and a large number of American destroyers and warships cross there," Abuhamzeh was quoted as saying on Friday evening by the semi-official news agency Tasnim."Vital American targets in the region have long since been identified by Iran...Some 35 US targets in the region as well as Tel Aviv are within our reach," he said, referring to Israel's largest city.'REVENGE ON THE MURDERERS'In Baghdad, many condemned the US attack, regarding Soleimani as a hero for his role in defeating the Islamic State militant group that had seized wide swathes of north and central Iraq in 2014."The broad participation in this procession proves the public's condemnation of America and its allies for their human rights abuses while claiming to fight terrorism," said one of the marchers, Ali al-Khatib."It is necessary to take revenge on the murderers. The martyrs got the prize they wanted - the prize of martyrdom."Some Iraqis at first reacted with joy to the US strike only to become quickly fearful of the fall-out, particularly for those involved in months of street protests against the Iranian-backed Baghdad government over alleged misrule and corruption.They said that Soleimani and Muhandis had backed the use of force against unarmed anti-government protesters last year and established militias that demonstrators blame for many of Iraq's social and economic woes.Protesters now worry they could become a target for reprisals from Shi'ite militias, who had been portraying the wave of anti-government demonstrations as a US conspiracy.