Iran's Supreme Leader Ayatollah Ali Khamenei said on Friday that Tehran does not need proxies in the region and that Yemen's Houthis, who are among the groups in the Middle East that Iran is aligned with, act on their own motivations.

U.S. President Donald Trump said on Monday he would hold Iran responsible for any attacks carried out by the Houthis, as his administration expanded the biggest U.S. military operation in the Middle East since he returned to the White House.

Over the years, Iran has been aligned with groups across the region that describe themselves as the "Axis of Resistance" to Israel and U.S. influence.

Those groups include Hamas, Lebanon's Hezbollah and various Shi'ite armed groups in Iraq.

Americans, said Khamenei, "make a big mistake and call regional resistance centres Iranian proxies. What does proxy mean?"
"The Yemeni nation has its own motivation and the resistance groups in the region have their own motivations. Iran doesn't need proxies," Khamenei said.

"They issue threats," added Khamenei, but "we have never started a confrontation or conflict with anyone. However, if anyone acts with malice and initiates it, they will receive severe slaps."

Experts on Yemen, where the Houthis expanded control during years of civil war, say the group seems mainly motivated by its domestic concerns and support base.