Jamaat-ud-Dawa offices have been closed down across the country
Police in Pakistan have arrested dozens of members of an Islamic charity the UN has listed a terrorist organisation in the wake of the Mumbai killings.
Members of Jamaat-ud-Dawa have been held across the country. India says it is a front for Lashkar-e-Taiba, the group it says was behind the attacks.
Last month's attacks on Mumbai left more than 170 people dead.
A key US envoy, John Negroponte, is in Delhi to tackle what the US still says is a "dangerous situation".
Separately, the Pakistani newspaper, Dawn, said it had tracked down the father of the sole surviving suspect in the attacks, quoting the man as saying he had been "in denial" but had now accepted his son, Mohammed Ajmal Amir Qasab, was the man being held.
In Mumbai itself, thousands of people joined hands on the streets on Friday to symbolise their unity in the aftermath of the attacks.
Police say that members of Jamaat-ud-Dawa have been detained in Sindh, Punjab, North-West Frontier Province (NWFP) and Pakistani-administered Kashmir, where the charity is reported to be especially active.
This is the truth. I have seen the picture in the newspaper. This is my son Ajmal
Sindh Home Secretary Arif Ahmed Khan told the AFP news agency that more than 40 people had been detained and 30 Jamaat-ud-Dawa offices had been sealed.
A spokesman for the charity in NWFP said that 150 people had been arrested and 42 offices closed.
Pakistan Defence Minister Ahmed Mukhtar said it had responded to the UN move because "we are part of the international community and cannot afford confrontation with the whole world".
He added: "Had we not implemented the resolution we would have been declared a terrorist state."
Hundreds of people meanwhile rallied outside the UN office in Muzaffarabad, the capital of Pakistani-administered Kashmir, to chant anti-US and anti-Indian slogans in protest over the closure.
The Jamaat-ud-Dawa leader, Hafiz Mohammad Saeed, who also founded Lashkar-e-Taiba, was put under house arrest on Thursday. He has strongly denied the allegations against him.
Tens of thousands of people took part in a human chain in Mumbai
The group's assets have been frozen, a senior government official said.
However the BBC's Syed Shoaib Hasan in Islamabad says that crucially the government has not yet formally banned the group, leading to accusations from some critics that it is reluctant to move it against it too quickly.
Mr Saeed's son, Mohammad Talha Saeed, said a legal challenge would be mounted in Pakistan's courts and possibly the International Court of Justice against the move to close the charity.
"There is no moral or legal justification for this action," he said.
'No bellicose talk'
In Delhi, Mr Negroponte met Foreign Minister Pranab Mukherjee a day after a visit to Islamabad.
Indian media reported that Mr Negroponte had handed over to Pakistan a list of organisations it wanted action taken against.
In Delhi Mr Negroponte said: "All of our diplomatic partners have a responsibility to contribute to this effort."
Pakistan said it was taking action but Foreign Minister Shah Mahmood Qureshi complained that "despite our requests, no evidence or information has been shared with [Pakistan's] government by India so far".
US Secretary of State Condoleezza Rice told CNBC she had heard "no bellicose talk" on her own visit to the two nations last week but added: "It is obviously a dangerous situation, and Pakistan needs to act and act forcefully."
In the Dawn article, the man who says he is Mohammed Ajmal Amir Qasab's father is quoted as saying: "I was in denial for the first couple of days, saying to myself it could not have been my son... Now I have accepted it.
"This is the truth. I have seen the picture in the newspaper. This is my son Ajmal," Amir Kasab said.
The paper said he was speaking from Faridkot, a village close to Deepalpur in Punjab province.
Amir Kasab said his son left four years ago, adding: "He had asked me for new clothes on Eid that I couldn't provide him. He got angry and left."
Meanwhile in Mumbai, organisers said that between 85,000 and 100,000 people linked in human chains at various locations - including the two hotels and main railway station that were attacked.
Organiser Dolphy D'Souza said: "The key purpose was to send a message that out of this despair and anguish... we are united, we want peace and nobody can create any wedge or difference to divide us. We are Indians first and last."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.