However, the BBC's Syed Shoaib Hasan in Islamabad says that while protests will continue throughout Pakistani cities and activists may try to reach the capital in small groups, the crackdown has effectively ended the "long march".
Protest organisers say that more than 1,000 opposition leaders and activists have already been jailed or put under house arrest.
Police in NWFP overnight arrested dozens of lawyers, political leaders, legislators and activists in the districts of Peshawar, Mardan, Abbottabad and Mansehra.
Raids are still going on in the area amid reports that many opposition leaders and lawyers have gone into hiding to avoid arrest.
Gatherings have been banned and large contingents of police have been deployed to prevent activists from proceeding to Islamabad in large groups.
Police also blocked a convoy of protesters led by the president of the Supreme Court bar association, Ali Ahmed Kurd, as it tried to enter Sindh province on its way to the capital.
Punjab and Sindh provinces have both banned political gatherings.
Mr Kurd said he "strongly condemned the Sindh government for stopping our peaceful march".
I don't think [President Zardari] will be able to complete his five years
He added: "We will try to reach Islamabad by other routes and appeal to all Pakistanis to reach Islamabad in groups or as individuals by any possible means.
"This action of the government has shown to the people of Pakistan and the entire world that lawyers cannot move freely in their own country."
On Thursday, the police in Karachi, the capital of Sindh province, baton charged to disperse protesting lawyers and political activists.
Lawyers in Karachi say they will boycott all courts on Friday.
The government fears the protest could turn more violent.
The US has expressed its concern about the situation.
In addition to the Holbrooke call, US ambassador to Pakistan Anne Patterson met Prime Minister Yusuf Raza Gilani.
US state department spokesman Robert Wood said the US was stressing that violence should be avoided, the rule of law respected and that peaceful protests should be allowed to proceed.
The protest follows a heightening of tensions in Pakistan, after a court ruling barring opposition PML-N party leader Nawaz Sharif and his brother from holding public office.
Mr Sharif has backed the lawyers' demand for the judges to be reinstated and has called on Pakistanis to join the demonstration.
Lawyers shout slogans during protests in Karachi
He said that Mr Zardari's refusal to meet the demand was "shortening his political life".
"I don't think he will be able to complete his five years," Mr Sharif said.
However, Mr Sharif said he had "no personal enmity with Zardari".
Mr Sharif confirmed he too had talked to Mr Holbrooke, adding: "There is no need for back channel diplomacy or private and secret dialogue. I have not slammed my doors on dialogue."
Some sources say the government may be willing to compromise on the governance of Punjab, the Sharif stronghold, and on some legal issues, but the role of former chief justice Iftikhar Chaudhry could still be problematic.
The sackings in November 2007 of some 60 senior judges, including Mr Chaudhry, sparked countrywide protests and ultimately led to President Pervez Musharraf's resignation.
Mr Zardari's critics argue that he fears the chief justice could revive corruption cases against him.
Six months after Mr Zardari took office, Pakistan is descending deeper into crisis, correspondents say.
The BBC's Barbara Plett in Islamabad says many believe that Mr Sharif's backing of the protesters has turned the march into a power struggle that the country can ill afford.
Are you in Pakistan? Are you planning to take part in the rallies? Have you been affected by the clashes in Karachi?
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