Iranian retaliatory operation has inflicted heavy losses on the US as well as the Israeli regime. (File photo)

The US military has confirmed that three American troops were killed and five others seriously wounded in Iranian attacks on American bases in the region.

In a statement on Sunday, US Central Command (CENTCOM) also confirmed that several more US troops sustained concussions and other non-fatal injuries.

The casualties are the first confirmed American deaths since the US and Israel launched a war of aggression against Iran early on Saturday, assassinating the Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei and many senior military commanders in Tehran and striking military and civilian sites across the country.

The offensive came about eight months after they launched unprovoked attacks on the country. Both offensives came while Tehran was engaged in diplomatic talks with Washington over its nuclear program.

Iran swiftly began to retaliate against the Saturday strikes by launching barrages of missiles and drone attacks on the Israeli-occupied territories as well as on US bases across the region.

Iran had repeatedly warned that US forces would be legitimate targets if Washington launched military strikes against the country.

The latest aggression against Iran came amid indirect nuclear negotiations between Tehran and Washington, with the third and last round taking place last week.