An FBI team arrived in Pakistan on Friday as the international probe into the failed Times Square bombing heated up and investigators focused on whether foreign terrorist money helped finance the operation, U.S. and Pakistani officials said.

The group of FBI investigators landed in Islamabad, where the FBI has a legal attache office that works with Pakistani law enforcement and intelligence officers, Pakistani officials said. Pakistani cooperation is considered crucial in nailing down the radical ties of Faisal Shahzad, the U.S. citizen charged in the attempted bombing.

Inside the United States, investigators were interviewing people who might have ties to Shahzad, but “no one is subject to imminent arrest,” said a senior U.S. law enforcement official who spoke on condition of anonymity.

Here and abroad, a key focus was the money trail. Investigators were tracking a money courier who may have helped funnel cash to Shahzad from overseas, but they cautioned that any links were uncertain.

Shahzad also may have obtained money to fund the Times Square operation from a hawala, an informal money-transfer network popular in South Asia and the Middle East that has been linked to al-Qaida and other terrorist groups, according to a former U.S. official briefed on the investigation.

“There is a lot of money,” said the senior law enforcement official, who noted that Shahzad brought $80,000 in cash into the United States when he returned from trips overseas between 1999 and 2008, and is thought to have additional sources of funds.

“To get that kind of money, the theory is you have someone help you move it,” the official said.

Several days after his arrest, Shahzad continued to cooperate with interrogators, to the point where they keep returning to ask follow-up questions, officials said.

One issue complicating the probe: Shahzad had multiple e-mail addresses, which is sending investigators into a web of thousands of messages they must track, which in turn lead to more e-mails and websites, officials said.

Investigators continue to believe that elements of the Pakistani Taliban trained Shahzad but are uncertain about his claims to interrogators that he met higher-ups within the group, including Pakistani Taliban leader Hakimullah Mehsud, U.S. officials said.

A senior Pakistani official said Friday that no evidence has emerged of ties between Shahzad and Mehsud, but there are “strong indications” that Shahzad, during his trips to Pakistan, was in touch with Jaish-i-Muhammad — an al-Qaida-linked group that is part of a mosaic of jihadist organizations in the country.

A federal law enforcement official said Friday that Shahzad had listened to speeches by radical Islamic clerics in the years since the Sept. 11, 2001, terrorist attacks.

Among those Shahzad has cited as inspiring him is Anwar al-Aulaqi, the American-born cleric in Yemen who has been tied to the suspect in the attempted Christmas bombing on a Detroit-bound plane as well as the man charged in last year’s fatal shootings at Fort Hood, Texas. Shahzad himself does not appear to have communicated with Aulaqi.

In Pakistan, authorities have arrested numerous militants, some of whom they think might be connected to Shahzad, and a Pakistani official said the government is engaged in a “hectic probe” to nail down any ties Shahzad may have had to militant groups in that country.