UPDATE 1-BA cancels flights to Pakistan indefinitely

(Adds detail, Pakistan International Airlines)

LONDON, Sept 23 (Reuters) - British Airways (BAY.L: Quote, Profile, Research) said on Tuesday it had cancelled flights to Pakistan indefinitely after a suicide truck bomb in Islamabad killed at least 53 people and heightened security fears.

The airline operates six direct flights from London to Islamabad every week.

"In light of the security situation in Pakistan we have cancelled our flights from Heathrow to Islamabad indefinitely," British Airways said in a statement.

"The safety of our customers, crew and aircraft is of paramount importance."

Pakistan International Airlines (PIA) (PIAa.KA: Quote, Profile, Research) is still operating four flights a week between London and Islamabad, according to a customer services representative.

The Czech ambassador and at least three other foreigners were among those killed in Saturday night's blast at the Marriott Hotel, Islamabad's worst bomb attack, which wounded scores and which security officials said bore the hallmarks of al Qaeda. (Reporting by John Bowker and Paul Hoskins, Editing by Opheera McDoom)