The Haqqani network, which Washington has blamed for a series of attacks in Afghanistan, may have been involved in a weekend bombing in Kabul that was the deadliest ground attack against Western troops in 10 years of war, officials said on Monday.
The suicide bombing on Saturday, which killed 13 foreigners, came just days before Afghanistan's President Hamid Karzai and senior officials from its neighbours and its Western backers, including U.S. Secretary of State Hillary Clinton, were due to meet in Istanbul to discuss regional security.
The involvement of the Haqqani group, believed by Washington to be based in the mountains of North Waziristan on the Afghanistan-Pakistan border, would make the already tough task of bringing Afghanistan and its neighbours together even more difficult.
We don't have any information indicating a direct Haqqani link yet, but it's very possible it is Haqqani-related, a Western diplomat said, speaking on condition of anonymity.
Officials said that while evidence of Haqqani involvement was by no means conclusive, the style of the attack and some of the equipment used in it raised that possibility.
Sirajuddin Haqqani, leader of the network, recently told Reuters that it is no longer based in Pakistan and is comfortable operating in Afghanistan after battlefield gains there.
A senior police official in Kabul said the explosives used in the attack were likely to have originated in either Iran or Pakistan.
If it's Pakistan, then it is definitely the work of the Haqqanis, but we are not certain as the investigation is underway, he said, also speaking on condition of anonymity.
Before, the Haqqanis claimed responsibility for unusual attacks in which they were indeed involved, but now they are seemingly avoiding independent claims of responsibility, and letting the Taliban get the credit, to avert future problems, the police official said.
ISAF said it was investigating Saturday's attack.
What we know so far is that the Taliban have claimed responsibility, ISAF spokesman Brigadier General Carsten Jacobson told Reuters. We are looking into the case whether there is Haqqani involvement and we will react appropriately.
The Taliban said it carried out Saturday's attack, in which Americans, Britons and a Canadian died, as well as three other civilians and a policeman.
Clinton visited the region earlier this month and said in Pakistan that the United States had earlier held a preliminary meeting with representatives of the Haqqani network.
That meeting was organised by Pakistan's powerful spy agency, the Directorate of Inter-Services Intelligence (ISI), which U.S. officials have repeatedly charged with playing a double game with Islamist extremists and working with the Haqqanis.
A European official, also speaking on condition of anonymity on Monday, said the sophistication and timing of the attack, coming so soon after Clinton's visit to Pakistan, indicated that it was likely the work of the Haqqanis.
It certainly has all the hallmarks of the Haqqanis, the official said. It's part of their efforts to resist efforts to bring them to the negotiating table.
Also attending Wednesday's security meeting in Istanbul will be foreign ministers from France, Germany and Poland, and representatives from NATO and the United Nations.
Turkey's President Abdullah Gul will host a trilateral meeting between Karzai and Pakistan's President Asif Zardari on Tuesday.
The Afghan government and its foreign backers are preparing for the end of 2014, the deadline for foreign combat troops to return home, though some foreign troops will stay on as trainers and advisers.
Some Afghans fear their own security forces will be unable to cope with the insurgency when the majority of foreign troops go and that their country may fall into another civil war.
(Reporting by Hamid Shalizi, Christine Kearney, Mirwais Harooni and Sayed Hassib; Editing by Sanjeev Miglani)