The Dutchman was suspended in October following an earlier comment about the conflict but had been cleared to return to training on Monday after showing remorse, the club had said.
However, El Ghazi posted a new statement on Wednesday that the German club said was 'incomprehensible' and that they would examine it from a legal perspective.
"My position remains the same as it was when this started," El Ghazi wrote.
"I am against war and violence. I am against the killing of all innocent civilians. I am against all forms of discrimination. I am against Islamophobia.
"I am against anti-Semitism. I am against genocide. I am against apartheid. I am against occupation. I am against oppression."
El Ghazi added that he had "no regrets or remorse" regarding his position and refused to distance himself from what he had previously said.
In a statement, Mainz said the player's contract had been terminated as a result of his statements and posts on social media without specifying.
"Stand for what is right, even if it means standing alone, The loss of my livelihood is nothing when compared to the hell being unleashed on innocent and vulnerable in Gaza," El Ghazi posted on Instagram later on Friday.
POST DELETED
El Ghazi, who joined Mainz in September and has also played for Aston Villa and Everton, was suspended on October 17th over his initial post which he has since deleted.
On Wednesday, however, he wrote: "I do not owe special responsibility to any state. I do not believe any people or states are beyond question and accountability, nor are they above international law."
"There can never be any justification for the killing of over 3,500 children in Gaza in the last three weeks ... I and we as a world cannot conscionably (sic) remain silent. We must call for an end to the killing in Gaza now."
Mainz said on social media on Wednesday that they had read El Ghazi's latest statement in relation to the club "which we noted with surprise and incomprehension.
"The club will check the issue legally and then evaluate it. The player registered sick on Monday and is currently not part of the training activity."
The Hamas attack on southern Israel on October 7th that triggered the hostilities killed about 300 soldiers and 1,100 civilians, Israel says.
Gaza health authorities say at least 9,227 people have been killed since Israel started its blitz on the enclave of 2.3 million people in retaliation for the Hamas rampage.
Mainz, without a league win this season, are bottom of the Bundesliga with three points and host RB Leizpig on Saturday.
