Fadi Ihsan Fadal, 33, is a Syrian-born Canadian from Montreal.
He was seized early on Wednesday while working for the New York-based relief group International Rescue Committee.
In a video released by his captors, Fadal identified himself as Ahmad Yassin Tikati, but his family saw the tape on television and quickly confirmed his identity, an IRC spokesman said.
"The man in the video is not Ahmed Yassin Tikati. It was our person, this is Fadi," said the spokesman, adding he did not know why Fadal had given a false name.
His brother, Ghayaf Fadal, told Aljazeera.net his family believed Fadi was forced to say he was an Israeli.
"But he has nothing to do with Israel," he said.
Fadi was kidnapped by armed men in the southern city of Najaf late on Tuesday, said Ghayaf. He is being held with a Palestinian, who apparently holds an Israeli identity card, identified as Nabil George Yacub.
The past few days "have been a nightmare", said Ghayaf. "We have no news, we don't know who took him or where they took him or how they are treating him."
Nightmare for family
A previously unknown group called Ansar al-Din said they captured the two and accused them of spying for Israel.
"We are a religious faction," a masked man said in the tape.
"He wanted to help in an Arab country"
Hostage Fadi Fadl's brother
Ghayaf said his brother had worked with underprivileged children in Sri Lanka and the Philippines. He was offered a position with International Rescue Committee (IRC), a US humanitarian organisation, in February to set-up a programme for underprivileged kids in Najaf.
"He wanted to help in an Arab country," said Ghayaf, adding he did not regret that Fadi went to the war-torn country.
"He was very happy with his work there. The community had accepted him," said his father, Ihsan.
"He doesn't deserve this," he said.
After a pause, he continued: "He went there to help children. Nothing else."
A fearful Yacub said he worked for RTI International, a North Carolina-based, independent non-profit organisation that has a major local governance contract in Iraq.
"I am Nabil George Yacub, an Israeli working for RTI," a
frightened-looking Yacub said.
Relatives in occupied East Jerusalem, where Yacub hails from, said he attended university in Georgia.
Asked by Israeli media if he had a message for the kidnappers, Yacub's uncle, Anton, said in Arabic: "We have been living under Israeli occupation since 1967. Like other Arabs in East Jerusalem, we have Israeli identity cards ... that doesn't mean we have any attachment to (Israel)."
Southern Iraqis are becoming
more hostile to foreigners
Razuk's status remains unclear. His family said he had an Israeli passport and was a citizen. However, Israeli Foreign Ministry spokesman Jonathan Peled said Razuk held an Israeli identity card, but was not a citizen.
Palestinians from occupied East Jerusalem are issued Israeli identity cards. They are eligible for Israeli citizenship, although few apply for it.
The Palestinian Authority said it would try to secure the release of both hostages.
Palestinian Cabinet minister Azzam al-Ahmad, a former ambassador to Iraq, said he had contacted Palestinian diplomats in Baghdad to try to win their release. Razuk's family had also asked Palestinian President Yasir Arafat to help secure the abductee's release.
Israel said it would not negotiate with the kidnappers.
"Israel should not feel responsible for their release. They did
not go to Iraq on an official visit," said Yuval Steinitz, chairman of parliament's defence and foreign affairs committee.
Luke Zahner, a spokesman for the US Agency for International Development, said in Washington Yacub was employed by RTI, which was doing work for USAID in Iraq.
A British civilian was also kidnapped this week in the southern Iraqi city of Nasiriya, the scene of heavy fighting between al-Sadr militiamen and Italian troops, said an occupation official on Thursday.
The official named the man as Gary Teeley, a British contractor. British media said Teeley, 37, was said to be a resident in the Middle East and had been working at a US airbase.
A Foreign Office official in London confirmed Teeley was missing, but would not say what he was doing in Iraq or comment on the manner of his disappearance.
In related news, occupation authorities refused to negotiate with "terrorists" who have been taking hostages in Iraq.
The US-led occupation has remained tight-lipped over the fate of the civilians kidnapped.