Democratic presidential hopefuls opposed President Donald Trump’s airstrike killing of Iranian commander, Gen. Qassem Soleimani, though the Pentatgon explained its defensive action is to protect American diplomats and service members in Iraq and throughout the region.

The U.S. Department of Defense announced that the U.S. military, at the direction of President Trump, killed Soleimani, the head of the Islamic Revolutionary Guard Corps-Quds Force, a U.S.-designated foreign terrorist organization, in Baghdad’s international airport in Iraq earlier on Friday, Jan. 3.

“General Soleimani and his Quds Force were responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more. He had orchestrated attacks on coalition bases in Iraq over the last several months—including the attack on December 27th – culminating in the death and wounding of additional American and Iraqi personnel,” the Pentagon said in a statement, adding that the Iranian general also approved the attacks on the U.S. Embassy in Baghdad this week.

“This strike was aimed at deterring future Iranian attack plans. The United States will continue to take all necessary action to protect our people and our interests wherever they are around the world,” said the statement.

Democratic presidential candidates raised their voices to oppose the measure, and took the chance to campaign for their White House race.

“No American will mourn Qassem Soleimani’s passing,” former Vice President Joe Biden said in a statement. “He deserved to be brought to justice for his crimes against American troops and thousands of innocents throughout the region.”

Biden criticized President Trump saying he has “just tossed a stick of dynamite into a tinderbox” with the killing of Iran’s top general, raising his concern that “Iran will surely respond” and the United States “could be on the brink of a major conflict across the Middle East.”

In his reaction, Sen. Bernie Sanders (I-Vt.) said in a tweet, “Trump’s dangerous escalation brings us closer to another disastrous war in the Middle East that could cost countless lives and trillions more dollars.”

Sen. Elizabeth Warren (D-Mass.) acknowledged “Soleimani was a murderer, responsible for the deaths of thousands, including hundreds of Americans,” but she said the killing of the Iranian commander is a “reckless move” which could escalate “the situation with Iran and increases the likelihood of more deaths and new Middle East conflict.”

Under President Trump’s order, at least three rockets were fired at Baghdad International Airport early on Jan. 3, killing seven Iranian officials, including Soleimani and Abu Mahdi al-Muhandis—deputy commander of the Popular Mobilization Forces.