WASHINGTON (Reuters) - At least three U.S. citizens, including a Brooklyn rabbi, were killed in militant attacks in the Indian capital Mumbai and the State Department said more Americans were at risk.

President George W. Bush said he was deeply saddened and the United States was working with India’s government to ensure the safety of those still under threat.

“We will continue to cooperate against these extremists who offer nothing but violence and hopelessness,” he said in a statement.

The Virginia-based Synchronicity Foundation said on its Web site that Alan Scherr and his 13-year-old daughter Naomi, Americans who were in India as part of a meditation program, had died in the attacks that have killed at least 124 people.

Separately, the New York office of the Chabad-Lubavitch Jewish group said a Brooklyn rabbi and his wife were killed in the siege on a Jewish center in Mumbai as part of the coordinated attacks. The rabbi was a dual U.S.-Israeli national and his wife Israeli, the group said.

“Rabbi Gavriel and Rivka Holtzberg, the beloved directors of Chabad-Lubavitch of Mumbai, were killed during one of the worst terrorist attacks to strike India in recent memory,” the Chabad’s New York headquarters said in a statement.

The couple’s son, who turns two on Saturday, escaped along with his nanny, the group said.

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State Department spokesman Gordon Duguid said: “There are still Americans at risk on the ground and we want to be very, very careful with any facts.”

At least 124 people have been killed and 284 wounded in the attacks on India’s financial hub.

Indian commandos on Friday stormed the Jewish center, killing two suspected Islamist gunmen but failing to save five hostages. Rescue efforts were still going on at the luxury Taj hotel where many foreigners stay while in Mumbai.

Duguid said a State Department hotline had received around 1,500 calls for information about friends and relatives.

U.S. consular staff are stationed at hotels affected by the attacks as well as hospitals in order to identify Americans in need of help as quickly as possible, he said.

Secretary of State Condoleezza Rice has over the past 36 hours spoken to India’s foreign minister as well as Pakistan’s President Asif Ali Zardari, said Duguid.

Rice also called U.S. President-elect Barack Obama twice to brief him, said Duguid. Aides to Obama said he had also received an intelligence briefing on the attacks.

Duguid said Rice had spoken to Zardari to “get a good sense of what is happening in the region.”

“Regional tensions have been a historical factor in South Asia and the United States has always worked for lessening those tensions,” he added.