There has been no official confirmation that a British man suspected of having played a key role in the London bombings is among the arrested. The British newspaper "The Guardian" reported today that Pakistani officials were questioning Haroon Rashid Aswat, seized four days ago carrying explosives, a British passport, and a lot of cash.
Agencies quote senior Pakistani security officials as saying that no significant arrests have been made and that there has not been any major breakthrough with regards to the London bombings.
The crackdown comes as Musharraf has called for a nationwide fight against extremism.
Since the emergence of evidence about a possible contact between the London bombers and Pakistani militant groups, Islamabad has been under intense international pressure to take action against Islamist militants.
At least one of the London bombers is believed to have attended a Pakistani madrassah, or religious school. On 18 July, British Prime Minister Tony Blair said Pakistan should deal with Madrassas that preach extremism.
"We have been working with the Pakistani government. We'll continue to do so, and obviously we are very anxious to make sure that the measures are taken that do deal with the extremist teaching in these places [madrassahs] and I am sure that it is of course in the interest of Pakistan as well because Pakistan suffers from this terrorism," Blair said.
Musharraf had vowed to root out extremism after the 11 September 2001 attacks on America. But Pakistani officials have acknowledged that Islamist extremist groups still operate in the country.
"Real Action This Time?" asked the headline of an editorial in today's Internet edition of "The News," a Pakistani newspaper.
Experts say that despite the flood of arrests, it is still too early to judge the severity of the new crackdown.
Farzana Shaikh is an associate fellow and an expert on Pakistan at Chatham House in London and an associate of the Cambridge University 's Centre of South Asian Studies.
"By all accounts, it appears to be a very rigorous and quite determined effort by President Musharraf to show the West that he is serious about what he says. I think it is too early to judge because we heard much of the same rhetoric just after 9/11, so I think we'll need a little more time [to judge]. After all, the crackdown has really just started," Shaikh says.
Shaikh adds there are limits to how far Musharraf, a general who seized power in a 1999 coup, can go in his campaign against extremism.
"The legitimacy of his regime has always been extremely fragile and he has had to depend upon religious parties, many of them with links to extremist groups, in order to bolster the credibility of his government. So this in some way can strain and limit his freedom of actions, but I think there is no question that many inside and outside the government feel that this [extremism] is a Frankenstein monster that has been let out and every effort has to be made to curb and control it," Shaikh says.
Some Pakistani papers report that most of the leaders of and activists of "defunct religious organizations" have fled underground to avoid arrest.
Police officials vow to track down these suspects. But Shaikh says officials face a difficult task.
"Since 9/11, many extremist groups which were banned immediately after that crackdown have resurfaced under new names, so it's really going to be very difficult for President Musharraf to extend the reach of his government in the way that I think he would like to," Shaikh says.
Pakistan's crackdown has sparked anger among fundamentalist Islamist parties.
The six-party hard-line Islamist alliance, the Muttahida Majlis-e-Amal (MMA), called for nationwide protests. A MMA senior leader, Liaquat Balochto, says rallies will be held "to denounce the 7 July attacks and the subsequent arrests by the military regime, which wants to fulfill its own secular agenda."
Pakistan's human rights commission has also weighed in, saying the government should not abuse people's rights in its fight against extremism.