Jamil Sayyed, Ali Hajj, Raymond Azar and Mustafa Hamdan were held without charge for their alleged involvement in the assassination of Hariri and several others in a massive bomb attack in downtown Beirut.
In an interview with the pan-Arab daily Asharq al-Awsat, President of the Special Tribunal for Lebanon Antonio Cassese said the detention of the generals was in line with Lebanese law.
"Under Lebanese law, somebody can be put in jail even if only suspected of a crime, without being charged, for as long as the inquiry is necessary," he explained.
Beirut had removed the arrest warrants on the four men earlier this month.
United Arab Emirates security officers arrested a suspect in the Hariri assassination, Mohammad Zuhair al-Siddiq, in the emirate of Sharjah as Beirut made preparations to release the generals.
There has been mounting speculation that the Hariri assassination was carried out with the support of allies to Syria. Damascus had a heavy hand in Lebanon during the decades-long civil war there, and Hariri held notably anti-Syrian views.
Cassese said the tribunal was preparing to make a special arrangement with Damascus in order to move forward with the investigation.
The tribunal is the first such body to examine the crime of terrorism. The trial is expected to last at least five years.