In a cell phone message to reporters, the little known group calling itself "Fedayeen al-Islam" - "Islam commandos" - referred to the owner of the Marriott by name.
"All those who will facilitate Americans and NATO crusaders like (owner Sadruddin) Haswani, they will keep on receiving the blows," said the message, which was in English.
It was impossible to verify the identity of the group or say whether it was in a position to make good on the threat. Pakistani officials were not immediately available for comment.
The group demanded that Pakistan break with Washington in an earlier message that claimed responsibility for Saturday's truck bombing at the Marriott in Islamabad, a blast that.
Little or nothing is known about the group. Pakistani officials suspect al Qaeda or Taliban militants carried out the bombing.
The attack underscored the threat posed by Islamic extremists, many of whom are based in the lawless, tribal regions along northwestern Pakistan's border with Afghanistan.
Concerned about the possibility of further attacks, the U.S. State Department has announced it's prohibiting all American government personnel from staying at or even visiting major hotels in Islamabad and the key cities of Karachi and Peshawar, and told them to stay away from restaurants as well. In addition, a notice from the U.S. Embassy in Islamabad urged American citizens working or visiting there to take similar precautions.
The U.S. has stepped up attacks on suspected militants in the frontier area, mostly by missiles fired from unmanned drones operating from Afghanistan. The incursions - especially a- have angered many Pakistanis.
On Wednesday, Pakistan's army said it had foundin South Waziristan, but denied claims by Pakistani intelligence officials that troops and local people shot down the aircraft.
The army statement said security forces recovered the drone, but it did not say anything about the plane's origin. It said a technical problem appeared to have caused the plane to crash and it was investigating.
The U.S.-led coalition in Afghanistan said one of its drones, which can be equipped with video surveillance equipment, went down Tuesday in the Afghan province of Paktika, bordering South Waziristan. But it said coalition forces retrieved the plane and no others were missing. The CIA also operates drones in the region.
Pakistani civilian leaders have condemned the cross-border operations by U.S. forces, while the army has vowed to defend Pakistan's territory "at all cost."
"We will not tolerate any act against our sovereignty and integrity in the name of the war against terrorism," Prime Minister Yousuf Raza Gilani told journalists. "We are fighting extremism and terror not for any another country, but our own country. This is our own war."
In the latest violence, a suicide bomber killed an 11-year-old girl and wounded 11 troops and some children in the frontier city of Quetta, officials said.
Security forces supported by helicopter gunships killed 20 militants in a second day of fighting near the town of Khar in another border area, Bajur, officials said. Just north of Khar, a roadside bomb killed two pro-government tribesmen and wounded several others.
Militant warlords have established virtual mini-states in the tribal belt, levying taxes and enforcing strict Taliban-style social codes and justice.
On Wednesday, a so-called "Peace Committee" executed four alleged murderers in Wana, the main town in South Waziristan, a witness said. Din Muhammed said members of the committee used mosque loudspeakers to summon a crowd before the four were shot.