Tensions between India and Pakistan were running high on Sunday morning as Delhi denied Islamabad's accusation that Indian planes had "inadvertently" violated Pakistani airspace yesterday.

The new dispute between the nuclear-armed neighbours came as Gordon Brown held talks with Manmohan Singh, the Indian Prime Minsiter, in Delhi before flying to Islamabad to meet Asif Ali Zardari, Pakistan's President, later this morning.

Mr Brown's trip is party of an international diplomatic effort, led by the United States, to prevent last month's attack on Mumbai, which India blames on Pakistani militants, from sparking a fourth war between India and Pakistan.

Pakistan's air force said on Saturday that Indian jets flew over the Pakistani-administered part of Kashmir and the eastern city of Lahore.

Lashkar-e-Taiba (LeT), the militant group that India blames for the Mumbai attack, is active in Kashmir and Jamaat-ud-Dawa – an Islamic charity seen as a front for LeT – has a complex just outside Lahore.

"We have confirmed it," said Sherry Rehman, Pakistan's Information Minister. "We have spoken to the Indian Air Force and they have said it was inadvertent."

"Our Air Force is on alert and ready to face any eventuality, but we do not expect this to escalate," she said. "There is no need for alarm."

However, Indian today denied that any of its aircraft had intruded into Pakistani air space.

"There has not been any airspace violation as has been alleged," said Wing Commander Mahesh Upasani, spokesman for the Indian Air Force.

India has been extremely careful in recent years to prevent its war planes from straying into Pakistan's airspace.

Pakistan shot down two Indian planes which it said had entered its airspace during the 1999 Kargil conflict, fought on the Line of Control dividing disputed Kashmir. India said the planes were in its airspace when they were shot down.

India this week called Pakistan the "epicentre" of terrorism and demanded it do more to crack down on militant groups on its soil, but ruled out military action.

After LeT militants attacked India's parliament in 2001, India and Pakistan massed troops on their common border, almost sparking their fourth war since they won independence from Britain in 1947.

Pakistan put its air force on high alert during the Mumbai attacks after someone pretending to be India's foreign minister made a phone call to President Asif Ali Zardari threatening war, according to officials and diplomats on both sides of the border.

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