The US embassy has warned that terrorist groups may have "established links" to a high-class catering company based in the Pakistani capital.
In an unusual email message to American residents in Pakistan, it said US government personnel had been instructed to avoid using the Hanif Rajput Catering Service, a well-known firm often used by foreign embassies in Islamabad.
The US embassy said the suspicions about the catering company have been shared with Pakistan government agencies. The message said Rajput was owned Rana Ashraf Khan and his son Salman Ashraf.
Earlier this week, a senior security official in Islamabad said that one of two people arrested over links to the failed Times Square car bombing was called Salman Ashraf. He identified him as the son of the owner of Rajput Catering Service.
A man who answered the phone at Rajput declined to comment.
A biography on the Rajput website said Salman Ashraf studied in Houston, Texas, before returning home to help run the family business. It said Rana Ashraf Khan worked for Pakistan International Airlines for 20 years and then started the catering firm. Rajput cooks for large parties, providing food, cutlery and tents at embassy compounds and the homes of the well-to-do in Islamabad.
Faisal Shahzad has been formally charged with terrorism and attempted use of a weapon of mass destruction over the incident on 1 May.