The Mumbai terror attacks threaten to chill improving ties between nuclear-armed rivals India and Pakistan just as the West is trying to get Islamabad to focus on al-Qaida and Taliban close to the Afghan border. India has not singled out Pakistan as being linked to the strikes, but Indian Prime Minister Manmohan Singh on Thursday said militants based outside his country carried them out. That was widely understood in Pakistan to be an accusation of its involvement. Defense Minister Ahmed Mukhtar said Pakistan "should not be blamed like in the past." "This will destroy all the goodwill we created together after years of bitterness," he told The Associated Press. "I will say in very categoric terms that Pakistan is not involved in these gory incidents." Deteriorating relations between Pakistan and India, which have fought three wars since 1947, would greatly complicate US foreign policy in the region. Incoming President-elect Barack Obama has said normalizing ties between the two South Asian neighbors will be a major plank of his broader campaign to stabilize Afghanistan and beat al-Qaida in the region. "You can't cozy up to a country that is accusing you of complicity in terrorism," said Shaun Gregory, an expert on South Asian terrorism at the University of Bradford in Britain. "Any sign of Pakistani involvement would be extraordinarily damaging." On Friday, Pakistani Prime Minister Yousuf Raza Gilani called his Indian counterpart and pledged his government's "full support to jointly combat extremism and terrorism," Gilani's office said. US Secretary of State Condoleezza Rice telephoned Pakistani President Asif Ali Zardari late Thursday to discuss ties and the regional situation, the Associated Press of Pakistan reported. In 2001, militants fighting Indian rule in the disputed Himalayan region of Kashmir attacked Parliament in New Delhi, helping push the countries to the brink of war a year later. It is widely believed that Pakistan used to provide material and tactical support to militants fighting Indian rule in divided Kashmir, but there has been less cross-border infiltration in recent years amid US pressure after the Sept. 11, 2001, attacks. India accused Pakistan's intelligence services of helping Taliban militants bomb its embassy in the Afghan capital in July, killing 58 people. Pakistani officials say there is no evidence to support the allegation. But relations between India and Pakistan have generally improved in recent years. Pakistan's new president, Asif Ali Zardari, declared over the weekend that India posed no threat to Pakistan and called for their heavily militarized border to be opened for trade. Some analysts speculated that the terrorists' goal may have been to trigger a collapse in India-Pakistan ties possibly to the levels of 2002, when New Delhi deployed tens of thousands of troops to the border. "In this situation, when all our energies are focused on fighting the militants, we cannot afford to shift our attentions to the eastern border" with India, said Ishtiaq Ahmad, professor of international relations at Quaid-i-Azam University in Islamabad. "This is a very risky moment." On Wednesday, teams of gunmen attacked at least 10 sites in India's financial capital of Mumbai, including two luxury hotels, a railway station and a Jewish center. More than 100 people were killed. In an address to the nation Thursday, the Indian prime minister said the group that carried out the attacks "was based outside the country" and warned its neighbors "that the use of their territory for launching attacks on us will not be tolerated." Earlier, Indian navy spokesman Capt. Manohar Nambiar said navy officers had boarded a cargo vessel it suspected of ties to the attacks that had come to Mumbai from Karachi, Pakistan. He later said the ship was not linked in any way to the strikes. While the investigation into the attacks is only just starting, many analysts said the terrorists were more likely to be indigenous Indian extremists blamed for a series of bombings this year than Pakistani-linked ones. Analysts also noted that India's government stood to benefit politically by hinting at the involvement of its old rival - rather than admitting some of its own 145 million Muslims had become radicalized. "It will always want to label this militancy as foreign rather than to accept it has its own problem," said Gregory, the South Asian terrorism expert. "That sells much more easily to the Indian public than admitting serious grievances within its Muslims." Indian media reports said a previously unknown group calling itself the Deccan Mujahideen claimed responsibility for the attacks in e-mails to several media outlets. There was no way to verify that claim.