By Luke Baker

LONDON, Dec 27 (Reuters) - The assassination of opposition leader Benazir Bhutto has thrown Pakistan into one of the worst crises in its 60-year history, raising the spectre of widespread civil unrest and the cancellation of elections.

Analysts say President Pervez Musharraf, who stepped down as army chief of the nuclear-armed country two weeks ago under intense international pressure, is likely to seize the moment to reimpose emergency rule and cancel, or at least postpone, elections scheduled for Jan. 8.

"It is fair to assume now that elections cannot go ahead," said Farzana Shaikh, an expert on Pakistan and an associate fellow at the Chatham House analysis group in London.

"The electoral process has been stopped dead in its tracks. I think there is a very real possibility that Musharraf will decide that the situation has got out of control and that he needs to impose emergency rule again.

She said Pakistan, a key U.S. ally in the battle against al Qaeda and the Taliban in Afghanistan, was entering "uncharted waters", which could lead to instability in a region that has seen three wars fought between Pakistan and its nuclear-armed neighbour India.

"This is not the first crisis Pakistan has faced since its inception in 1947, but I would be inclined to say that it is the worst convergence of crises we have seen," Shaikh said.

Bhutto, 54, died in hospital after being targeted in a combined shooting and suicide bomb attack as she campaigned in the city of Rawalpindi among thousands of supporters.

The attack killed at least 15 other people and came hours after supporters of Nawaz Sharif, another contender in the January elections and a staunch opponent of Musharraf, came under fire from gunmen, with three people killed.

"VERY, VERY DANGEROUS"

While Islamic hardliners, including members of the Taliban and al Qaeda, both of which operate in Pakistan, have been named as possible perpetrators of the attack, analysts said Bhutto's political opponents and those close to Musharraf's political party could not be ruled out of suspicion.

"It's going to be very difficult to establish the truth of who was behind this," said M.J. Gohel, the executive director of the Asia-Pacific Foundation, a security and intelligence think-tank in London.

"As well as the Taliban and al Qaeda elements, there are many other candidates -- there are elements within the military and elements within the intelligence services, which never had a good relationship with Bhutto.

"There are of course political opponents as well -- she had a lot of enemies within Pakistan as everyone knows."

Shaikh pointed to the fact that Bhutto was killed in Rawalpindi, which is a long way from the North West Frontier province where Islamic militants usually operate.

"That will raise fears that there was some level of official negligence that permitted this attack to go ahead," she said. "These sorts of events are going to raise very serious concerns about whether there was some sort of official connivance."

Bhutto's campaign managers have complained frequently that not enough was being done at a national level to protect her.

She narrowly escaped assassination on her return from exile in October when a suicide bomber blew up her campaign bus, killing 139 people.

Gohel said that as well as the domestic repercussions of Bhutto's assassination -- angry supporters clashed with security forces in the hours since her death -- there were widespread international concerns as well.

"The ramifications are enormous," he said. "There will now be more violence and if Musharraf imposes another state of emergency there could be further crackdowns and protests.

"We are looking at a political vacuum if the elections don't take place. The radical Islamists could really start occupying that vaccuum and operating from within it.

"Pakistan is a country that is home to al Qaeda and the Taliban and is also obviously home to nuclear weapons and long range missiles... all of which have repercussions for the West and the world." (Additional reporting by Adrian Croft; Editing by Ibon Villelabeitia)

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