Pakistani President Asif Ali Zardari had a minor heart attack and is undergoing treatment in a Dubai hospital, a source said on Wednesday, fueling rumours he may resign.

Zardari's office, however, said, he was in hospital for routine tests. It said a news web report, which triggered much of the speculation, was untrue.

Financial markets were unaffected by the rumours.

'President Zardari is in a Dubai hospital for medical tests and checkup as planned,' presidential spokesman Farhatullah Babar told Reuters.

'Reports in some sections of the media speculating on the president's activities and engagements are speculative, imaginary and untrue.'

But a Pakistani source in Dubai familiar with the president's condition told Reuters that Zardari had suffered a minor heart attack.

'Two days ago, he had chest pain' and decided to go to Dubai, the source said. Six years back too Zardari had a minor heart attack, the source said. 'Since then, he has been on medication,' he added.

A Dubai-based member of Zardari's Pakistan People's Party, Mian Muneer Hans, said the president landed in Dubai around 7.30pm on Tuesday.

'He walked to his car in the airport and was not on any ambulance,' said Hans, adding that he was accompanied by his doctor and petroleum minister Asim Hussain. Zardari was taken straight to the American Hospital in Dubai, said Hans.

'He's taking rest in the hospital now. He may be there for two to three days,' he added.

The hospital's chief executive officer Thomas Murray, contacted by Reuters, declined to comment on the reports.

Hans, however, said the medical visit was 'a routine check for his heart.'

The rumours about his health and possible resignation swirled on Twitter and other social media. 

'Some elements blew this up to create unrest in the country,' said Fauzia Wahab, a senior member of Zardari's Pakistan People's Party. 'His visit to Dubai and having a medical check up is perfectly normal.'

Pakistan's civilian government has been under extreme pressure in recent weeks following the resignation of its ambassador to Washington over an alleged memo to the Pentagon asking for help in forestalling a feared coup attempt in May.

Tension between the government and military have bedevilled the nuclear-armed South Asian country for most of its existence, with the military ruling the country for more than half of its 64-year history after a series of coups.

Relations with the US have been rocked by a year of bust-ups despite some $20 billion in security and economic aid to Pakistan since 2001, much of it in the form of reimbursements for assistance in fighting militants.

First there was the jailing of a CIA contractor for shooting dead two Pakistanis in the city of Lahore.

Then there was the secret US commando raid inside Pakistan that killed al Qaeda leader Osama bin Laden, and then came US accusations that Pakistan was involved in attacks on American targets in Afghanistan.

It was also further rocked by a November 26 Nato strike on two Pakistani border posts that killed 24 soldiers, infuriating the country's powerful military which also has a tense relationship with Zardari.-Reuters