The development came as city officials in Brussels cancelled public celebrations for the turn of the year, including New Year's Eve fireworks displays, citing "continuing terror threat".
The last three of the six people arrested during raids on Thursday in and around the Belgian capital "have been released after interrogation", the federal prosecutor s office said in a statement.
In at least two capitals - Turkey's Ankara and Belgium's Brussels - officials also said they had disrupted plots to strike at New Year's celebrations that stretch into today.
Belgian broadcaster RTL said Saouti founded the motorcycle club called Kamikaze Riders and that Karay was also a club member.
It has identified the men as Said S., 30, and Mohammed K., 27.
The men denied the charges against them, the lawyers added.
During the searches, no weapons or explosives were found, but military-type training uniforms, IS propaganda material and computer equipment were impounded and are being examined, the prosecutor's office said. Their main quarry, however, was not there: Abdelhamid Abaaoud, who went on to become the suspected ringleader of the November 13 attacks in Paris.
The first three in the group were already released hours after their arrests on Thursday. They charged him with terror offences.
On Wednesday, Belgian police arrested a tenth suspect over those killings, during a house search in the capital.
The two were then charged with threatening to carry out terror attacks, recruiting people to carry out such attacks and direct involvement in the activities of an alleged terrorist group.
The increased threat of terrorist attacks due to Islamic extremism is near the forefront of every discussion on security, especially following the deadly attacks in Paris and San Bernardino.
Last year, some 100,000 people turned out to watch the traditional New Year's Eve fireworks display.
Officials said the plot revealed Tuesday was not directly linked to the wave of bombings and shootings on a Paris concert venue, bars, restaurants and the national stadium.