The government has been accused of security lapses over Lahore
Pakistan is facing a "mortal threat" from internal militancy, UK Foreign Secretary David Miliband has said.
Mr Miliband told the BBC that politicians must unite to face a "very grave situation" that was worsening.
He was speaking as Pakistan continued to probe this week's attack on the Sri Lankan cricket team in Lahore.
Pakistani police have released sketches of four of some 14 gunmen suspected of involvement in the ambush that left six policemen and a driver dead.
Mr Miliband told BBC Radio's Today programme that Pakistan's internal instability was "a grave situation and... it has got worse".
He pointed to the fallout between President Asif Ali Zardari and former PM Nawaz Sharif, who was last week banned from elected office by the Supreme Court.
Mr Miliband urged politicians to unite, saying: "I think that the degree of political disunity that exists at the moment is only contributing to the problem."
He added that country's economic decline in the global credit crunch was also a major factor.
Mr Miliband said it was not known who carried out the Lahore attack but he said that the Lashkar-e-Taiba militant group had "deep roots in the Punjab".
He urged the central and local governments to take action against groups he described as "front organisations" for Lashkar-e-Taiba.
Police in Pakistan are still working on an interim report into the Lahore attack.
Police chief of Punjab province, Khaled Farooq, told AFP news agency "a little more time is required to complete the investigation" but that it would be finished in the next 24 hours.
Provincial governor Salman Taseer said on Thursday that "we have identified the people who did the operation".
There has been much speculation in the media since, with some reports pointing the finger at Lashkar-e-Taiba and others at al-Qaeda and the Taleban. Dozens of people have been held for questioning.
A spokesman for Lashkar-e-Taiba, Abdullah Ghaznavi, told AFP the reports of his group's involvement were "false, incorrect and baseless".
Pakistan's interior ministry chief Rehman Malik increased speculation by saying he could "not rule out [the involvement of a] foreign hand in the incident".
The head of Interpol, Ronald Noble, has arrived in Islamabad but his talks with Mr Malik were scheduled to be about November's Mumbai attacks.
Indian Foreign Minister Pranab Mukherjee on Friday said the Lahore attack showed "the [Pakistan] government's lack of will or capability in tackling this menace".
The Pakistani government has come under fire for the security it provided for the Sri Lankan team.
Umpires travelling in a bus behind the cricketers have said they were left unguarded. English match referee Chris Broad said they were "sitting ducks".
Two in the bus were Australian and Prime Minister Kevin Rudd said on Friday: "I am sufficiently concerned about what has been said by the Australians that we need an explanation, and we intend to get one."
Pakistan's cricket circles have reacted angrily to the security complaints.
Pakistan Cricket Board chairman Ijaz Butt accused Mr Broad of "fabrication".
On Friday, former cricket star Javed Miandad said the International Cricket Council should ban Mr Broad for life.
The Commissioner of Lahore, Khusro Pervez, has also defended the police response to the attack.
But he did admit that there were "certain security lapses which are very vivid and very clear".
"The gunmen were meant to be combated by backup police support, which didn't arrive," he said, "and the vehicles used for escorting the Sri Lankan convoy were not adequate."
The attacks are expected to have massive ramifications for the cricket world, with the ICC considering whether Pakistan can co-host World Cup matches in 2011.