Israel has said that 13 UN employees in Gaza were arrested but later made it clear that the detentions took place over the past four years.
The Israeli army picture alleged to show a Palestinian militant loading a rocket onto a UN ambulance
Israeli General Yisrael Ziv announced the arrests on Tuesday.
But an army spokesman said the UN staff were among those detained since the start of the Palestinian intifada.
News of the arrests surfaced as Israel appeared to row back from its claims that militants used a UN ambulance in Gaza for a rocket strike on Israel.
Army spokesman Capt Jacob Dalal said the information about the UN arrests had been taken out of context.
"They are among all the people arrested in the course of the conflict," he told Reuters. "Some may be held and some may not."
UN officials in New York said they had no information about the latest reported arrests but said that in the 12 months to June this year, 34 Unrwa staff were arrested or detained by Israeli authorities in the West Bank and Gaza.
Most were held without charge and Unrwa did not receive any official information about the reason for their detentions.
Confusion over the arrests came when Gen Ziv told a news conference: "We have in our hands a list of 13 detainees who are to be indicted, they are UN people with suspected links to terrorism."
The news conference was called in the midst of a row between the UN and Israel over Israeli claims that footage showed a UN ambulance being used to transport rockets.
When he was asked about whether the object filmed was a rocket or a stretcher, Gen Ziv said: "I suggest we don't deal with the object but rather with the context," Haaretz newspaper reported.
Haaretz also reported that the Israeli army officers believe it is " impossible to swear" the object was not a stretcher.
UN Secretary-General Kofi Annan is sending a team to investigate the accusations.
Peter Hansen, head of the UN Relief and Works Agency for Palestinian refugees (Unrwa), has acknowledged that some of Unrwa's 24,000 Palestinian employees were probably members of militant groups but he did not see that as a crime.
Not every Hamas member is a militant, Mr Hansen told the Canadian Broadcasting Corporation on Monday.
But he said the UN expected all employees to act with neutrality.