U.S. officials were working out details with Indian diplomats on Friday for the departure of a team of FBI agents to join the investigation of the Indian terror attacks that killed at least 150 people.

Among the dead were an American rabbi and his wife and a man and his teenage daughter who were traveling with a group from a Virginia meditation community, U.S. authorities said.

A second group of investigators was on alert to join the first team if necessary, said the officials, who spoke on condition of anonymity because of the sensitivity of the operation.

The investigators aim to learn more about the origins of the militants who carried out the lethal strikes on luxury hotels, a train station and an Orthodox Jewish center where the rabbi and his wife were among five hostages slain.

President George W. Bush said in a statement that his "administration has been working with the Indian government and the international community as Indian authorities work to ensure the safety of those still under threat. We will continue to cooperate against these extremists who offer nothing but violence and hopelessness."

His statement expressed sadness for the deaths and injuries of Americans.

"We also mourn the great loss of life suffered by so many people from several other countries, and we have the wounded in our thoughts and prayers," Bush said in the statement released at Camp David, his presidential retreat in the mountains north of Washington.

Bush also expressed condolences to Indian Prime Minister Manmohan Singh in a telephone call.

Secretary of State Condoleezza Rice telephoned her Indian counterpart, Foreign Minister Pranab Mukherjee, on Friday to discuss the Mumbai situation, State Department spokesman Gordon Duguid said.

He gave no details of their conversation but said American lives remained in peril in Mumbai.

U.S. officials were checking with Indian authorities and hospitals to learn more about the extent of casualties.

The State Department urged Americans not to travel, at least through the weekend, to the stricken city, India's financial capital and the home of the Indian movie industry.

In New York, the Chabad-Lubavitch movement confirmed Friday that Rabbi Gavriel Noach Holtzberg, a dual Israel-U.S. citizen, and his wife, Israel-born Rivka Holtzberg, were killed during the terrorist assault on the ultrareligious group's Mumbai headquarters, one of the attackers' 10 targets in South Mumbai.

The couple's toddler son, Moshe Holtzberg, survived the assault after he was taken from the center by an employee. He was with his grandparents.

Rabbi Moshe Kotlarsky, vice chairman of the educational arm of Chabad-Lubavitch, praised the couple for their work in India.

"As emissaries to Mumbai, Gabi and Rivky gave up the comforts of the West in order to spread Jewish pride in a corner of the world that was a frequent stop for throngs of Israeli tourists. Their selfless love will live on with all the people they touched. We will continue the work they started."

Bobbie Garvey, a spokeswoman for the Synchronicity Foundation, the meditation group in Virginia, identified the two slain members as Alan Scherr, 58, and his 13-year-old daughter, Naomi.

The meditation group said in a statement that four other members of the 25-person group, two Americans and two Canadians, who were staying at the Oberoi Hotel were wounded by gunfire and were believed in stable condition.

A South Asia specialist said Friday that the terror "group itself is probably drawing from, in large numbers, Indian operatives, but it probably enjoys a fairly healthy support of Pakistan."

"The big picture is that there's probably going to be more of this, not less of this, to come," the specialist, Christine Fair of the RAND Corp., said Friday. "I don't think this is the most lethal attack that terrorists have perpetrated, but it is certainly the most expansive, in its scope and its scale and its perplexity."

Pakistan's ambassador to the U.S., Husain Haqqani, said in a statement that his country is "confronting the menace of terrorism with great vigor." Haqqani insisted "it is unfair to blame Pakistan or Pakistanis for these acts of terrorism even before an investigation is undertaken."

Democratic U.S. Sen. Russ Feingold urged restraint to avoid unnecessary tension in the South Asian subcontinent. "As we continue to learn the details about the attacks and those responsible for them, we must not allow them to undermine the progress that has been made to foster better relations between India and its neighbor Pakistan," said Feingold, a member of the Senate's foreign relations and intelligence committees.

He described India and Pakistan as "critical partners in our global fight against terrorism."

A U.S. counterterror official also cautioned that it was premature "to reach any hard-and-fast conclusions on who may be responsible for the attacks." But the official, who spoke on intelligence matters on condition of anonymity, added that "some of what we're seeing is reminiscent of past terrorist operations undertaken by groups such as Lashkar-e-Tayyaba and Jaish-e-Mohammed."

Those two groups are Pakistani militants who have fought Indian troops in Kashmir and are reported to be linked to al-Qaida.

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AP reporters Matthew Lee, Pamela Hess and Sharon Theimer in Washington, Tom Breen in Richmond, Virginia, Juanita Cousins in Nashville, Tennessee, and Adam Goldman in New York contributed to this story.

