"Last night, a slap in the face was delivered," Ayatollah Ali Khamenei said in a speech broadcast live on state television.

His remarks came after he had vowed "severe revenge" for a US drone strike that killed Iranian military commander Qasem Soleimani near Baghdad international airport last week.

Shortly after midnight, Iran fired a series of missiles at bases in Iraq housing US troops, officials in Washington and Tehran said.

"One important issue is what is our duty now?" following Soleimani's assassination, said the supreme leader.

"An important incident has happened. The question of revenge is another issue," said Khamenei.

"Military actions in this form are not sufficient for that issue," he said, referring to the assassination.

"What is important is that America's corrupt presence must come to an end in this region."

Soleimani was one of Iran's most popular public figures. He was laid to rest in his hometown early on Wednesday morning after massive funeral processions in several major cities of Iran.