"We will not give up, will not stop, will not be silenced, until a just verdict and punishment is found," al-Maliki said after visiting a Halabja cemetery where he spoke to gas attack victims and their relatives.
Gas attack trials
Ali Hassan al-Majeed, a cousin of Saddam known as "Chemical Ali" for his use of poison gas, is on trial for the Halabja gas attacks, along with three men including former defence minister, Sultan Hashem, and former army chief of staff, Hussein Rashid Muhammed.
Majeed, Hashem and Muhammed have already received death sentences for their role in the Anfal military campaign in which tens of thousands of Kurds were killed in the 1980s.
But political wrangling has so far prevented the death sentences
from being carried out.
Iraq's Presidency Council, consisting of President Jalal Talabani, a Kurd, and his two deputies, a Sunni and a Shia, has not ratified the Anfal sentences because of a row over whether Hashem and Muhammed were guilty.
Tareq al-Hashemi, the Sunni Arab vice president, says they were just carrying out orders and should be treated as soldiers.
US troops have intervened in standoffs between Kurdish Peshmerga soldiers and Iraqi forces over disputed territory and US officials see the tensions between the Arab-led Baghdad government and the KRG as the greatest threat to Iraq's security.
The United States has urged the two to work towards peace.
Al-Maliki's Arab-led government has called oil deals the KRG has made independently with foreign firms illegal and disputes KRG claims to territories along its border.
Barzani has accused al-Maliki of acting like a tyrant and sidelining the Kurd minority. On Sunday the two leaders agreed to hold further talks.