The Palestinian Central Elections Commission began work in Gaza on Wednesday after Hamas gave the organisation access to its offices, its chief said.
"We began our work on Wednesday at the commission's headquarters in Gaza after receiving access to them last night," CEC chief electoral officer Hisham Kuhail told AFP.
Until now, the CEC offices have been locked and the keys held by Gaza's Hamas rulers, meaning electoral officials have been unable to begin preparing for elections that are meant to take place in May.
Under the terms of a reconciliation deal signed by Hamas and rival Fatah movement in May last year, legislative and presidential elections are to be held within a year of the accord being signed.
But the CEC needs to update the voting register in Gaza, which has not been done since the last elections in 2006.
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And the commission has warned it needs weeks to prepare its offices and train staff before it can even start on the process of registering voters and updating its documents.
The commission also cannot start the registration process without an official order from president Mahmud Abbas, an instruction usually issued three months before planned elections.
The delay in the reopening of the CEC's Gaza offices has raised fears it may be logistically impossible to hold the elections in May, as stipulated in the reconciliation agreement.
On Monday, a senior Palestinian MP who heads one of the committees responsible for implementing the unity deal, warned the vote could not be held on time.
"According to the Palestinian Central Elections Commission, it has become impossible to hold the elections this May, and we will have to work fast to hold the elections this year," Mustafa Barghuti told AFP.