US ally in the campaign against militancy but also a breeding ground for Islamist violence.
Pakistan has detained at least six people suspected of ties with the abortive bombing attempt, including Salman Ashraf, who worked for a catering company servicing embassies, according to a security official.
His father, Mohammad Ashraf Khan, who co-owns Hanif Rajput Catering Service, said in an interview that his son, 35, had no relations with the Times Square suspect, Faisal Shahzad.
"The nature of our job is such that one can meet anyone, anywhere," said Khan, but the company had no ties to terrorism.
US authorities say Shahzad, a Pakistani-American, has admitted to the would-be Times Square bomb attack and has been cooperating with investigators since his arrest on May 3.
American and Pakistani authorities are likely scrambling for clues on whether those detained have ties to militants in Pakistan, who are bent on toppling the state and are violently opposed to the US presence here.
The United States has said Pakistan Taliban militants allied with al Qaeda were behind the attempted New York attack.
The US embassy in Pakistan issued a warning to US government personnel and American citizens on Friday about the catering company, saying it may have terrorist links.
"They (the US embassy) were our client from the very first day (of our business), since 1991. They booked a function the day before yesterday but cancelled it yesterday," said Khan.
He said clients of the company, located on the first floor of an ordinary office building in a commercial area of Islamabad, also included Pakistani military officials.
Studied in United States
The company provides services to top-flight functions in the capital, including embassy receptions and corporate events.
Ashraf, the company's vice-president, left Pakistan for the United States in 1997 to study and graduated with a computer sciences degree from the University of Houston in 2000, according to his father.
Khan said he himself was an aeronautical engineer and worked for Pakistan International Airlines and Saudi Arabian Airlines before going into the catering trade.
Norwegian mobile operator Telenor said one of its staff at its Pakistani unit had been detained by Pakistani authorities over the bomb plot.
"Faisal (Shahzad) lived in Ashraf's Islamabad house for some time," said a Pakistani security official.
"We are investigating whether Ashraf has provided any financial support to Faisal because Ashraf and his father are rich people and they run a very big catering business."
Khan denied Shahzad had ever lived in their house.
"He was not religious. He didn't attend Friday prayers regularly," said a neighbour of Ashraf.
His cousin, Faheem Khan, who also works in the same office as a manager, described him as a very "pleasant personality".
"He only wears, jeans and casuals. He is very fond of movies, especially Western movies. He also loves PlayStation."
Another Pakistani official said one of the people detained was identified as Ahmed Raza and was Ashraf's friend and business partner. He also runs his own catering service.
Shoaib Mughal, said to run a big computer business in Islamabad, was also being held, said an official.
"He was believed to have phoned Shahzad to tell him to return home after the Times Square incident," said the official. Relatives of Mughal who work at his business declined comment.