Chief UN investigator Detlev Mehlis wants to question the former security chiefs, who are pro-Syria, the Lebanese officials said on Tuesday, speaking on on condition of anonymity.
The detainees were: Maj. Gen. Jamil Sayyed, the former chief of General Security; Maj. Gen. Ali Hajj, the former director general of the Internal Security Forces; and Brig. Gen. Raymond Azar, the former director general of military intelligence.
They have previously been questioned by chief investigator Mehlis, a German prosecutor.
Mehlis also asked for former legislator Nasser Qandil, a staunch supporter of Syria, to be detained for questioning, the officials said.
Legislator in Syria
But when police went to Qandil's house in Beirut, he was not there and his wife said he was in Syria, the officials said.
A fifth person, Brig. Gen, Mustafa Hamdan, the pro-Syrian head of Lebanon's Presidential Guards, was told he must come to Mehlis's office for questioning, the officials said. Hamdan turned himself in soon after.
Hamdan has previously been questioned by Mehlis.
A UN team is probing al-Hariri's
Al-Hariri and 20 others were killed in a massive bombing that targeted his motorcade in a Beirut street on 14 February.