The United States government has placed advertisements in the main newspapers in Pakistan offering a reward of up to two million dollars for information leading to the conviction of those responsible for killing four American oil executives last November.

The men, together with their driver, were shot dead in Karachi shortly after a Pakistani citizen was convicted in the United States of murdering two CIA agents.

It's not the first time Washington has offered such a reward -- it did so in March 1995 after two US diplomats were killed in Karachi.

This time the adverts say the US government might be prepared to relocate anyone who gives vital information.