With Pakistan’s civilian government clinging to power in the face of deepening internal divisions, a new book by a former CIA officer says Pakistan is the most dangerous place on earth and should be President Obama’s top national-security priority. 

“It is the fastest growing nuclear arsenal in the world and it has more terrorists per square mile than any other country in the world,” Bruce Riedel, author of “Deadly Embrace: Pakistan, America and the Future of Global Jihad” tells FOX News in an exclusive interview. “Pakistan is our most important partner in the war against Al Qaeda and the most difficult partner in the war against Al Qaeda.” 

The U.S.-Pakistani relationship has been a fraught one from the day the South Asian nation broke free from British control to become an Islamic republic in 1947. Since President Dwight Eisenhower made the first presidential visit to Islamabad in 1951, America has valued the strategic importance of the nation but been frustrated by the divided loyalties of the government there. 

There are many examples of the double game that Pakistan has played with its U.S. ally.  One example was in 1993, it was Pakistan’s Western-educated Prime Minister Benazir Bhutto who helped North Korea make major advances in its nuclear program.  Riedel’s book describes how she shared the secrets that helped the North Koreans develop a uranium enrichment program and, ultimately, a nuclear weapon. 

"She carried back and forth information about nuclear centrifuges from North Korea to Pakistan and other information. Whether she carried a nuclear weapons design, I don't think that has been substantiated one way or another,” said Riedel, who led a White House strategy review on Pakistan for Obama in 2009. 

“It's very ironic: Mrs. Bhutto was probably the most secular, pro-Western Pakistani politician of our lifetime and yet she was also involved in the nuclear trade with North Korea. And she was one of the early sponsors of the Afghan Taliban." 

Bhutto reportedly received ballistic missile designs for her country’s ongoing arms race with neighboring India in return for the nuclear secrets. The allegations first appeared in a book written by British journalist Shyam Bhatia, who was a friend of Bhutto's from Oxford. 

In “Goodbye, Shahzadi” Bhatia writes: "The gist of what she told me was that before leaving Islamabad she shopped for an overcoat with the deepest possible pockets into which she transferred CDs containing scientific data about uranium enrichment which the North Koreans wanted." 

He says she told him not to publish the information until after her death, highlighting her constant fear that she could be assassinated, which she was in December 2007. 

In another example of the complicated relationship between the U.S. and its troublesome ally Pakistan the CIA has never yet been allowed to interview the father of Pakistan's nuclear program, A.Q Kahn, who in 2004 admitted to providing nuclear know how to, among others, Iran, Libya and North Korea. 

Khan lives in Islamabad and has been free from house arrest since early 2009. 

Critics of the administration’s current policy suggest that the Obama team has not taken a tough enough line when it comes to the suspected ties between the nation’s military and intelligence organizations and the Taliban and other radical groups. 

KT McFarland, a nuclear proliferation and national security expert who worked in the Reagan Pentagon, said that the U.S. must be more demanding with its troublesome ally. “We've let the Pakistanis tell us what they want, and frankly they are playing both sides,” said McFarland, a FOX News contributor. 

“On one hand, they are helping us in Afghanistan and with Al Qaeda against the Taliban, but on the other hand they are helping the Taliban too, because they are hedging their bets.” McFarland suggested that the U.S. should tell the Pakistani government to get serious about the search for Osama Bin Laden, who is believed to be hiding in the mountainous eastern region of the country. “I think we need to go to Pakistan and say, ‘Look, you guys have had almost 10 years. We know that Osama Bin Laden is in Pakistan. If you want the relationship to continue, we want Osama Bin Laden.’” 

Riedel, now a fellow at the Brookings Institution think tank, says the U.S. must pursue a two-track approach with Pakistan. On one hand, he supports a five-year, $1.5-billion non-military aid package sponsored by Sen. John Kerry and Sen. Richard Lugar that is still stalled in Congress. 

The money, Riedel says, will help convince the Pakistani people that the U.S. is seeking a long-term friendship. But Riedel also says the U.S. should get tough with Pakistan’s top generals and members of its intelligence service, the I.S.I., if there is evidence they are supporting the Taliban or Al Qaeda. 

He suggests placing offending officers on the U.S. terror watch list, which means their overseas assets would be frozen. “Imagine a state with the fastest growing nuclear arsenal in the world, the sixth largest army, that’s an active sponsor…of terrorist groups…that welcome Osama bin Laden and Al Qaeda out of their hiding places into the Presidential palaces in Islamabad,” Riedle said. 

“That’s the nightmare that we have to worry about. And that’s the nightmare that we have to avoid at all costs.”

Jennifer Griffin currently serves as a national security correspondent for FOX News Channel . She joined FNC in October 1999 as a Jerusalem-based correspondent. You can follow her on Twitter at @JenGriffinFNC.