Al-Qaeda in Iraq carried out the triple bomb attack which killed at least 56 people in Jordan's capital Amman, a statement posted on the internet says.
Jordan's Deputy Prime Minister, Marwan Muasher, said earlier the militant group was a "prime suspect".
Nearly 100 people, mostly Jordanians, were injured in the blasts at the Grand Hyatt, Radisson and Days Inn hotels.
Most of the dead are Jordanians but a number of other Arabs, two Chinese, one American and an Indonesian also died.
At least several hundred people have marched through Amman to denounce the bombers and show loyalty to King Abdullah II.
"Burn in hell, Abu Musab al-Zarqawi," they chanted, referring to the Jordanian-born militant believed to lead al-Qaeda in Iraq.
At least one placard read "Jordan's 9/11" - a reference to the 2001 terror attacks on America.
The claim from al-Qaeda in Iraq appeared on a website generally used to post such announcements.
It said the hotels were targeted because they had become favourites with "American and Israeli intelligence and other Western European governments".
Jordan, a key US ally in the Middle East, has become a base for Westerners who fly in and out of Iraq for work and has long been regarded as a prime target for attack, correspondents say.
Giving details of casualties on Thursday, Mr Muasher said 56 people were known to have died along with the three bombers, and 96 were wounded.
Earlier reports had suggested about 300 people had been hurt in the blasts.
DNA tests were being used to identify at least 14 bodies, including those of the bombers, he said.
Two bombers seem to have used devices strapped to their bodies while the third used a car bomb.
The Jordanian government has declared a day of national mourning for the victims, known to include two Palestinian Authority security officials.
The bomb attacks were condemned "in the strongest terms" at the UN Security Council.
UN Secretary General Kofi Annan is due to arrive in Amman on Friday, after delaying a scheduled visit by one day.
Wedding party attacked
In the worst attack, hundreds of guests were enjoying a wedding reception at the Radisson SAS when the bomb went off.
The bride and groom each lost a parent and were themselves injured.
"There were a lot of injured people and some dead people," the groom, Ashraf al-Khaled, said.
"I lost my father and my father-in-law on my wedding night."
Security has been tightened around Amman and Jordan's land borders have been closed.
Roadblocks were set up around hotels and embassies, and Prime Minister Adnan Badra ordered all schools and public offices to close on Thursday.
1. Vehicle explodes outside hotel after being stopped at a police checkpoint
2. In the most deadly attack, a bomb destroys a banquet room where a wedding reception was being held. Dozens injured by shrapnel
3. Suicide attacker detonates bomb in hotel bar, just before 2100 local time. Two senior Palestinian officials are among the dead