Colombia is one of the world's largest producers of cocaine

Surveillance aircraft were withdrawn two years ago after the accidental downing of a civilian plane over neighbouring Peru with the loss of two lives.

But Secretary of State Colin Powell has given the go-ahead to resume flights and President George W Bush is expected to announce the move on Thursday, officials said.

The announcement is not expected to cover similar flights over Peru.

Operation Airbridge Denial had supplied information from US surveillance equipment to local air force planes for them to intercept suspected drug flights.

In April 2001, a Peruvian fighter strafed the plane of US missionary Veronica Bowers, killing both her and her seven-month-old daughter Charity.

Three others aboard the plane survived.

A US-Peruvian investigation did not assign blame but concluded that guidelines developed by both governments to prevent such an occurrence had been ignored.

The US Senate Select Committee on Intelligence put the incident down to poor planning and judgement, and recommended its suspension.

Reward for Uribe

The announcement of new flights, the BBC's Rob Watson reports from Washington, is being timed to coincide with the first anniversary of Colombian President Alvaro Uribe's entry into office.

It is being seen as a reward for Mr Uribe whose tough line against the country's militant groups and drug-traffickers has impressed Washington.

The Colombian leader pressed for the resumption himself when he visited President Bush in April.

"Uribe really wants this on Thursday," one unnamed US official told AFP news agency.

"I think we'll try to accommodate him."

Mr Powell reportedly made his recommendation after lengthy talks with Colombia on safety procedures.