The man, described by Aljazeera as the spokesman of the Islamic Army in Iraq, held the US responsible for the car bombs that have killed thousands of civilians since 2003 in course of the interview broadcast on Saturday.
The man, whose face was blurred but who was identified as Ibrahim al-Shemmari, said: "The security bodies of the Islamic Army ... follow them constantly or at least keep watch and occasionally a journalist or another falls into their hands."
He said the group's interrogators questioned those captured and a court-like body issued its verdict and sentence.
"If he was found innocent he would be freed and if he was caught red-handed in a certain situation with the occupation then he would be handled in a manner that is in line with the interests of jihad in Iraq," added the man.
The man described Enzo Baldoni, the Italian journalist killed by his group in 2004, as a spy, and said journalists and other non-military foreigners were not targets "so long as they were committed to their professions".
"The Italian? He was a spy. It was clear to us from the beginning that he was a spy. Evidence were abundant but the French journalists were freed," he said of two French journalists his group released after abducting them in 2004.
Italian Baldoni was killed by the
Islamic Army in Iraq in 2004
More than 200 foreigners and thousands of Iraqis have been abducted in the anarchy that followed the US-led invasion.
Most foreign hostages have been released, but 54 are known to have been killed and more than 50 are believed to be held.
The Islamic Army in Iraq has claimed several kidnappings and attacks on foreign and Iraqi government forces.
But "it is not within our targets to kill innocent civilians", said the man.
"There is information that many of the car bombs are the work of the Americans ... they have long been working to distort the reputation of the resistance so that the Iraqi people would reject it," he said.
Thousands of people have been killed by car bombs in Iraq since the March 2003 US-led invasion.
Al-Shemmari dismissed the Iraqi government as a group of "sectarian gangs at whose hands the Sunnis tasted bitterness", and said his faction would not negotiate with Iraqi officials.
The Islamic Army would, however, negotiate with the US if it recognised what he called the resistance and set a timetable for its withdrawal from Iraq.
"We do not reject negotiations (with Americans) in principle as these would be negotiations for the exit of the occupiers," he said.