"Pakistan will provide all possible assistance to her," Sadiq told The Associated Press.
Siddiqui, 36, who has been described as a possible "fixer" for al-Qaida, was picked up in Afghanistan on July 17.
According to a U.S. criminal complaint, she was carrying documents containing recipes for explosives and chemical weapons and describing "various landmarks in the United States, including New York City."
The complaint also alleges Siddiqui carried "chemical substances in gel and liquid form that were sealed in bottles and glass jars." It did not elaborate.
The day after Siddiqui was detained, as a team of FBI agents and U.S. military officers prepared to question her, she allegedly snatched a soldier's rifle and pointed it at an Army captain. She fired two shots but missed because an interpreter pushed the weapon aside, authorities allege.
She was wounded when a soldier fired at her in response. She was given medical aid and later flown to New York to be formally charged in a federal court.
In 2004, then-Attorney General John Ashcroft and FBI Director Robert Mueller III said Siddiqui was one of seven people ths FBI wanted to question about suspected ties to al-Qaida.
Siddiqui is believed to have returned to Pakistan shortly after the Sept. 11, 2001, attacks in the United States and later disappeared. Her family has insisted she is innocent of terror-related accusations.
Over the years, there has been speculation that the U.S. or Pakistan had secretly detained Siddiqui. Sadiq on Sunday said he had no information on whether Siddiqui had ever been in Pakistani custody, while a U.S. Embassy spokesman strongly denied the allegation.
"The United States did not have knowledge of her whereabouts until she was detained by the Afghan police on July 17," spokesman Lou Fintor said. "Ms. Siddiqui was not in custody of the United States either at Bagram Air Base in Afghanistan or anywhere else at any time prior to her detention on July 17.
"Any rumors or allegations to the contrary are absolutely baseless and without any credible foundation whatsoever." Sadiq has said Pakistan also was seeking information on the whereabouts of Siddiqui's three children, who were reported missing along with her.
According to the state-run Associated Press of Pakistan, a Pakistani diplomat assured Siddiqui in their meeting Saturday that the country would do its best to ensure she received fair treatment and proper medical care.
U.S. authorities say Siddiqui received a biology degree from the Massachusetts Institute of Technology and wrote a doctoral thesis on neurological sciences at Brandeis University, outside Boston, and that she could have used her knowledge of the United States to support terrorists trying to slip into the country and plot attacks.