With the chant "Bowing to American demands is treason", hundreds marched on Tuesday to protest against a possible miscarriage of justice due to US diplomatic pressure.
Naim Abu Ful, Bashir Abu Laban, Muhammad Hamad and Ahmad Abd al-Safi were brought before a closed military court on Saturday charged with responsibility for a roadside bombing in October that killed three American security men in Gaza.
Former minister and current MP Imad al-Faluji told protesters that the trial of the four was "political" and also called for their release.
"We are in favour of the law, a state of rights and justice and we will not witness such injustice in silence."
US Ambassador to Israel Daniel Kurtzer has also criticised the hastily convened military trial.
The diplomat said any trial should not be held behind closed doors and the charges should be tougher.
The Popular Resistance Committees, a resistance group that carried out attacks against Israeli troops in the occupied Gaza Strip for over three years ago, has identified the four suspects as members.
But it has also denied involvement in the 15 October bombing.
"We urge President Arafat to free our men," a spokesman for the Popular Resistance Committees said at the Gaza rally, which was organised by the group and drew nearly 500 people on to the streets.
The trial at the military court in Gaza City was called without notice, days after US officials complained the Palestinian Authority had not cooperated fully in the
investigation of the bombing.
A military prosecutor said the four were involved in planting bombs against Israeli troops in the area where the convoy attack took place and this "might have led to the killing of the Americans as a result of the bombs that were planted".
Palestinian police bomb have
uncovered little evidence
At the beginning of Saturday's court session, two of the suspects shouted that they had nothing to do with the bombing.
Kurtzer said Washington should have been told in advance of the Gaza trial. "We don't believe that this is the way to proceed," he told a convention of American rabbis in Jerusalem on Monday. "We want to see an open trial".
Also on Tuesday a Palestinian resistance group said it had killed a man accused of collaborating with Israeli security forces.
Al-Aqsa Martyrs' Brigades named the dead man as Tahsin Abu Arkub of Ram Allah in the West Bank. His body was delivered to a city hospital on Tuesday.
"We shot him dead with four bullets to the head and chest in Ram Allah because he was a collaborator who has helped Israel kill and detain many Palestinians," an al-Aqsa representative told journalists.
Palestinians have killed dozens of fellow countrymen accused of helping Israeli forces put down an uprising for independence that erupted in September 2000.
Arafat has condemned the killings and last week ordered a special committee to investigate the recent killing of another suspected collaborator in Ram Allah.