The new spokesperson for the Islamic Army in Iraq and Jaish al-Mujahidin, Dr Ibrahim Yusuf al-Shimmari, told Aljazeera that the decision comes in the context of the groups' plans to implement a political programme and be politically recognised.
"It is most appropriate for the two groups to unite and appoint a media spokesman," said al-Shimmari, "due to the escalating amount of persons who claim to speak on behalf of the resistance and adopt political projects that do not serve the resistance."
This is the first step in the implementation of the groups' plan to unite, added al-Shimmari. "Other steps will follow soon."
The Islamic Army late last year captured and subsequently released two French journalists, Christian Chesnot and Georges Malbrunot. The group had demanded that France lift its ban on headscarves in the country's schools.
The group has also captured foreigners and Arabs working for companies in Iraq that are allegedly linked to the US government.
The Jaish al-Mujahidin has claimed responsibility for the kidnapping of Indonesian journalists in February as well as attacks on US forces.
Christian Chesnot was one of two
French reporters captured in Iraq
Al-Shimmari refused to clarify whether the groups' members included Iraqis as well as Arabs from other countries, saying "every armed group has its secrets and we cannot reveal all of them at once".
He however added: "We are all sons of the Iraqi people. It is not strange if we unite in order to face our enemy. That is why the situation does not require us to bring fighters from outside the country to defend Iraqi land and its dignity."
US talks denied
Asked to comment on any attempts to involve many other groups in their coalition, al-Shimmari would only say: "Unity is a political vision of the Iraqi resistance. There are many practical steps that will be achieved concerning this issue."
Al-Shimmari has also denied reports of any talks between US forces and armed groups in Iraq.
"I assure you ... that no contacts have been made directly or indirectly with the Americans"
Dr Ibrahim Yusuf al-Shimmari
Islamic Army and Jaish al-Mujahidin spokesperson
"The US announcements are nothing but lies. If talks with US forces are useful and in accordance with our political programme, we would have announced this to all our people.
"I assure you," he added, "that no contacts have been made directly or indirectly with the Americans."
The spokesman also said that "the United States carries out vast military operations, devastating vast areas of our land and then it says it has held talks with the fighters".
"This is nothing but deception to pretend that it is a realist administration that holds talks to reach an agreement."