Iraq and Iran on Wednesday exchanged the remains of 31 soldiers killed in the 1980-1988 war between the two countries which have since become allies, the Red Cross said.

"Under the auspices of the #ICRC, the remains of 11 Iraqi & 20 Iranian soldiers were repatriated to their respective homelands today," the International Committee of the Red Cross said on Twitter.

It said the exchange took place at the Shalamcheh border post in the Basra region of southern Iraq.

"We will continue to support relevant authorities in providing answers to families of the #missing," since the UN-brokered ceasefire that ended the war, it said.

Several exchange ceremonies have been held in past years, with hundreds of remains being transferred to their home countries under a 2008 accord with the ICRC.

"Over 30 years have passed since the end of the conflict and thousands of families on both sides still remain in the dark on the fate of their loved ones," the ICRC said in April.

The war cost hundreds of thousands of lives on both sides, but Iran has become increasingly influential in Iraq since the 2003 US-led invasion that toppled Iraqi dictator Saddam Hussein.