The United States and India urged Pakistan Tuesday to do more to counter extremist groups operating from its soil as the world's two largest democracies announced measures to strengthen security and energy ties.

Speaking on a visit to New Delhi, US Secretary of State John Kerry declared that ties once clouded by suspicion had progressed "amazingly" in the last two years and echoed President Barack Obama's description of their relationship as "the defining partnership of the 21st century".

India and the United States have a common goal in creating a counterbalance to the rise of China and hold regular top-level dialogue in Delhi and Washington under a formal strategic partnership.

But a flare-up in violence in Kashmir meant that India's arch-rival Pakistan featured prominently in talks between Kerry and his counterpart, Sushma Swaraj.

After Foreign Minister Swaraj reiterated long-running accusations that Pakistan was "providing safe havens to terror groups," Kerry also urged Islamabad to do more to combat extremists operating from its territory.

He said it was vital Islamabad moved to "deprive any group of sanctuary", highlighting the threat posed by Lashkar-e-Taiba, a Pakistan-based Kashmiri separatist group behind a string of anti-Indian attacks.

"We will not and we cannot make distinctions between good and bad terrorists... Terrorism is terrorism," Kerry said at a press conference alongside Swaraj.

Kerry said the US government had "had conversations with all members of the region frankly about efforts they need to take against terrorism which comes out of their country", adding that he had personally raised the issue with Pakistan's Prime Minister Nawaz Sharif.

India has accused Pakistan of stoking a new bout of unrest in Kashmir, the troubled Himalayan region which has been divided between the two countries since independence in 1947 and is claimed in full by both.

Around 70 civilians have been killed since the beginning of last month in the aftermath of the Indian army's killing of a charismatic young separatist leader and a curfew remains in place in many parts of Kashmir.

Swaraj said there was "a meeting of minds" during her talks with Kerry on tackling the threats posed by extremists as she reiterated long-standing accusations that Pakistan was sponsoring "cross-border terrorism".

"We repeated our stand that Pakistan should stop providing safe havens to terror groups... We also agreed that countries must not categorise terrorists as good or bad," said the Indian foreign minister.

Both sides said that there had been an agreement to step up cooperation on intelligence.

"We agree on additional measures to strengthen our counterterrorism," said Swaraj. "We will intensify intelligence sharing."

- Nuclear progress -

In an illustration of the burgeoning cooperation, Kerry announced plans to revive trilateral talks between India, Afghanistan and the United States.

He also said there had been an agreement "to move forward" on long-standing plans for six nuclear reactors which he said would provide electricity to tens of millions of people, without giving more details.

The deal involving US giant Westinghouse has been held up in the past by concerns over an Indian law that would make US companies liable for accidents at plants they helped build.

The start of Kerry's two-day visit came only hours after the two sides signed an agreement in Washington that allows access to each other's military bases for repairs and resupplies.

US Defense Secretary Ashton Carter and his Indian counterpart Manohar Parrikar sealed the pact in efforts to strengthen defence ties to counter concerns over China's growing military assertiveness.

Carter said the agreement would make joint operations between their militaries logistically easier and more efficient.

Washington has increasingly turned its focus to Asia as it tries to counter China's growing clout in the South China Sea, and is eager for India to play a greater role in a network of defence alliances.

The two sides are also keen to expand business ties, with the US targeting an increase in two-way trade from $100 billion to $500 billion.

US Commerce Secretary Penny Pritzker, who is accompanying Kerry, praised recent reforms by the Indian government which has moved to ease caps on foreign direct investment in a range of business sectors.

"As a result of the reforms, the US and India trade more with each other, invest more in each other, and do more business together than ever before," she said.