Ammar al-Dwaik, director of the central elections commission (CEC), said armed men burst into two of its branches in the Gaza Strip and the West Bank city of Nablus, in some cases opening fire, but causing no casualties.
"We have told all our employees to close and leave their offices," al-Dweik said on Tuesday.
The CEC said armed men had fired shots at the offices, destroyed equipment and verbally and physically assaulted staff members.
It said the suspension would stay in place "until further notice and until it receives assurances that the safety of CEC personnel will be guaranteed".
The move means candidates who want to register for the 25 January election will be prevented from doing so until further notice. The registration process was due to expire at midnight on Wednesday.
Armed group's raids
Security sources in Gaza said armed men from al-Aqsa Martyrs Brigades, whose followers are loyal to the ruling Fatah faction, had burst into at least four CEC offices - in Gaza City, Bait Lahia, Khan Yunus and Rafah.
Another group of al-Aqsa Martyrs Brigades' armed men burst into CEC offices in Nablus, where they made off with a computer.
A Fatah official said Palestinian Authority president and Fatah leader Mahmoud Abbas did not rule out postponing the election altogether during a meeting of the party's central committee late on Tuesday.
The office in Khan Yunis was one
of four that was raided
Abbas indicated that he would delay the vote if the elections commission advised him that the security situation was not favourable, said the official who requested anonymity.
Despite the security concerns, the committee agreed to put Prime Minister Ahmed Qurei at the top of its electoral list.
Over the past few days, al-Aqsa Martyrs Brigades' armed men have stepped up a series of raids on offices of the commission.
The unrest is thought to be linked to a growing dispute within Fatah over the composition of its list of candidates for the legislative elections, which has always been subject to heated wrangling.
A statement from Abbas's office said he "strongly condemned the aggression against the CEC offices and its personnel".
Abbas had ordered the security services "to take the necessary measures to arrest the perpetrators and to ensure the security of the CEC's personnel and offices".
But he also urged the CEC to resume its work in saving the elections and ensuring the success of the Palestinian democratic process.
Al-Aqsa Martyrs Brigades wants
al-Barghuti to head the Fatah list
Abbas's office announced late on Tuesday that the Fatah list would be unveiled on Wednesday.
An al-Aqsa Martyrs Brigades statement released in Gaza accused Fatah's leadership of selecting unpopular candidates close to the ruling elite, at the expense of those who had been chosen during the partial primaries over the past few weeks.
It called for the legislative election "to be delayed" to enable the party to hold organised primaries.
It also insisted that the Fatah list be headed up by Marwan al-Barghuti, the jailed leader of the Palestinian uprising.
The statement read: "Any list which is not led by our brother in arms Marwan Barghuti does not represent Fatah and we will not accept it."
Fatah sources said the central committee was likely to elect either al-Barghuti or Prime Minister Qurei as head of its list.