The body of Gen. Qassem Soleimani, who was killed in a U.S. drone strike, arrived Sunday in Iran to throngs of mourners, as President Donald Trump threatened to bomb 52 sites in the Islamic Republic if Tehran retaliates by attacking Americans

Soleimani’s death Friday in Iraq further heightens tensions between Tehran and Washington after months of trading attacks and threats that put the wider Middle East on edge. The conflict is rooted in Trump pulling out of Iran’s nuclear deal with world powers, an accord likely to further unravel as Tehran is expected to announce as early as Sunday it will break another set of limits.

Iran has promised “harsh revenge.” Already, a series of rockets launched in Baghdad late Saturday fell inside or near the Green Zone, which houses government offices and foreign embassies, including the U.S. Embassy.

Trump wrote on Twitter afterward that the U.S. had already “targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture.”

Trump did not identify the targets but added that they would be “HIT VERY FAST AND VERY HARD.”

Iran is talking very boldly about targeting certain USA assets as revenge for our ridding the world of their terrorist leader who had just killed an American, & badly wounded many others, not to mention all of the people he had killed over his lifetime, including recently....

— Donald J. Trump (@realDonaldTrump) January 4, 2020

....targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD. The USA wants no more threats!

— Donald J. Trump (@realDonaldTrump) January 4, 2020

Democratic presidential candidate Joe Biden, campaigning in Iowa, questioned whether Trump was acting alone or with support of allies. “We have no idea – I have no idea – whether he has any plan at all,” the former vice president told reporters Saturday night. “But when he makes statements like that, it just seems to me to be he’s going off on a tweet storm on his own, and it’s incredibly dangerous and irresponsible.”

After thousands in Baghdad on Saturday mourned Soleimani and others killed in the strike, authorities flew the general’s body to the southwestern Iranian city of Ahvaz, according to the state-run IRNA news agency. An honor guard stood by early Sunday as mourners carried the flag-draped coffins of Soleimani and other Guard members off the tarmac.

Officials brought Soleimani’s body to Ahvaz, a city that was a focus of fighting during the bloody, 1980-88 war between Iraq and Iran in which the general slowly grew to prominence. After that war, Soleimani joined the Guard’s newly formed Quds, or Jersualem, Force, an expeditionary force that works with Iranian proxy forces in countries like Iraq, Lebanon and Yemen.

Authorities also plan to take Soleimani’s body to Mashhad later Sunday, as well as Tehran and Qom on Monday for public mourning processions, then onto his hometown of Kerman for burial Tuesday.

Soleimani was the architect of Iran’s regional policy of mobilizing militias across Iraq, Syria and Lebanon, including in the war against the Islamic State group. He was also blamed for attacks on U.S. troops and American allies going back decades.

Though it’s unclear how or when Iran may respond, any retaliation was likely to come after three days of mourning declared in both Iran and Iraq. All eyes were on Iraq, where America and Iran have competed for influence since the 2003 U.S.-led invasion.

After the airstrike early Friday, the U.S.-led coalition has scaled back operations and boosted “security and defensive measures” at bases hosting coalition forces in Iraq, a coalition official said on condition of anonymity according to regulations.

Meanwhile, the U.S. has dispatched another 3,000 troops to neighboring Kuwait, the latest in a series of deployments in recent months as the standoff with Iran has worsened. Protesters held demonstrations in dozens of U.S. cities Saturday over Trump’s decisions to kill Soleimani and deploy more troops to the Mideast.

In a thinly veiled threat, one of the Iran-backed militia, Asaib Ahl al-Haq, or League of the Righteous, called on Iraqi security forces to stay at least a kilometer (0.6 miles) away from U.S. bases starting Sunday night. However, U.S. troops are invariably based in Iraqi military posts alongside local forces.

Iraq’s government, which is closely allied with Iran, condemned the airstrike that killed Soleimani, calling it an attack on its national sovereignty. Parliament is meeting for an emergency session Sunday, and the government has come under mounting pressure to expel the 5,200 American troops who are based in the country to help prevent a resurgence of the Islamic State group.

Also Saturday, NATO temporarily suspended all training activities in Iraq due to safety concerns, Canadian Defense Minister Harjit Sajjan said.

The U.S. has ordered all citizens to leave Iraq and temporarily closed its embassy in Baghdad, where Iran-backed militiamen and their supporters staged two days of violent protests in which they breached the compound. Britain and France have warned their citizens to avoid or strictly limit travel in Iraq.

No one was hurt in the embassy protests, which came in response to U.S. airstrikes that killed 25 Iran-backed militiamen in Iraq and Syria. The U.S. blamed the militia for a rocket attack that killed a U.S. contractor in northern Iraq.