Britain is working with the US to ensure a ceasefire between India and Pakistan endures and that "confidence-building measures" and dialogue take place, foreign minister David Lammy said on Saturday.

Pakistan has said Britain and other countries, in addition to the United States, played a major role in de-escalating the worst fighting in decades between the nuclear-armed South Asian rivals, which erupted last week.

A rapid diplomatic effort to broker the ceasefire succeeded on May 10, but diplomats and analysts say it remains fragile.

"We will continue to work with the United States to ensure that we get an enduring ceasefire, to ensure that dialogue is happening and to work through with Pakistan and India how we can get to confidence and confidence-building measures between the two sides," Lammy told Reuters in Pakistan's capital Islamabad at the end of a two-day visit.

Pakistan and India fired missiles onto each other's territory during weeks of tensions after a deadly attack on tourists in the contested region of Kashmir that New Delhi blames on Islamabad. Pakistan denies involvement.

US President Donald Trump said after the ceasefire was struck that talks should take place in a third-country venue but no dates or location for the talks have been announced.

"These are two neighbours with a long history but they are two neighbours that have barely been able to speak to one other over this past period, and we want to ensure that we do not see further escalation and that the ceasefire endures," Lammy said.

Asked about India's suspension of the Indus Water Treaty, potentially squeezing Pakistan's water supply, Lammy said: "We would urge all sides to meet their treaty obligations."

Delhi said last month it had "put in abeyance" its participation in the 1960 pact, which governs use of the Indus river system, a move Pakistan says it would consider an act of war if it disrupted access to water in the agriculturally dependent nation.

Lammy said Britain would also continue to work with Pakistan on countering "terrorism", saying that it is "a terrible blight on this country and its people, and of course on the region."

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'OBFUSCATION' BY RUSSIA ON UKRAINE

Lammy accused Moscow of obfuscating after talks between Ukraine and Russia on a possible ceasefire ended in less than two hours and Trump said "nothing could happen" until he had met directly with Russian President Vladimir Putin.

"Yet again we are seeing obfuscation on the Russian side and unwillingness to get serious about the enduring peace that is now required in Ukraine," Lammy said. "Once again Russia is not serious."

"At what point do we say to Putin enough is enough?" he said.