A U.S. congressman arrived here yesterday on a personal mercy mission to win the release of an American couple held hostage by Abu Sayyaf gunmen in the southern Philippines.

Republican Representative Todd Tiahrt arrived aboard a private jet in the city of Zamboanga and was immediately whisked to the military's southern command amid tight security for a meeting with Defence Secretary Angelo Reyes and top generals.

Officials said he has requested permission to travel to nearby Basilan island to personally assess the operations being conducted by some 5,000 soldiers to rescue Martin and Gracia Burnham, who hail from Tiahrt's state of Kansas, and were seized in May.

The Burnhams, along with Filipina nurse Deborah Yap, are among the last of a group of hostages seized by the Abu Sayyaf in a kidnapping spree this year. A third American, Guillermo Sobero of California, was beheaded by the gunmen earlier this year along with more than a dozen Filipino hostages.

"We are encouraging close cooperation between (the) American army and Philippine troops. We have already seen great steps in that direction," Tiahrt told reporters. He said "greater cooperation" would be "very beneficial to the way the two hostages are released."

Defence Secretary Reyes said Tiahrt expressed concern on the progress of the rescue operations, after the military missed a self-imposed deadline to rescue the hostages by Christmas.

But the Philippines understands that Tiahrt is "under strong pressure" from his constituents to recover the hostages, Reyes said, even as he defended Filipino troops as "good and excellent soldiers" capable of solving the crisis.

Before leaving the U.S., Tiahrt had said he would urge President Gloria Arroyo to allow U.S. special forces to join the hunt for the hostages, who are believed to be in a thickly-forested, mountain area in central Basilan.

"The rescue operation is not a simple matter. Look at (U.S.) efforts to capture Osama bin Laden in Afghanistan – it's (been) three months and until now he is still at large," Reyes, a former military chief of staff, told reporters here.

"Our southern command elements cannot just go there in Basilan and bomb the hell out of them because of the hostages. We do not want a situation where the operation is successful but the hostages are dead," he stressed.

He also ruled out participation of U.S. special forces in combat, but said American military experts could be involved in training programmes and the assessment of operations on the ground.

U.S. military advisers earlier this year trained a company of Filipino troops for elite counter-terrorism operations who are now operating in Basilan.

Another group of military advisers would also be arriving in Zamboanga next month to train more Filipino soldiers and set up a communications facility "to be used to assist us," Reyes said.

"The pressure for us to finish this sad episode in our history is great and we are responding positively to this pressure, although it's taking longer than expected," Reyes said.

Security forces meanwhile continue tracking down a kidnapped U.S. missionary couple and a Filipino nurse held by Abu Sayyaf gunmen in Basilan island, as troops try to beat a self-imposed military deadline before New Year's Day.

"We will continue the rescue efforts whether it's Christmas or New Year's Day," said Brig. Gen. Glicerio Sua, in-charge of the rescue operation.

The military earlier imposed a deadline before Christmas to free the Burnhams and the Filipino nurse, but failed. The deadline has been extended to December 31 and officials remain optimistic.

The rebels originally demanded $2 million, but eventually lowered this to $1 million in exchange for the safe release of the American hostages.

Both the Philippines and the U.S. have rejected any payment of ransom, saying it would not deal with terrorists.

"We hope that this hostage crisis would be resolved soon. We really do not care about the Christmas season because we are more concerned in accomplishing the rescue mission," Sua said, adding: "If we resolved this crisis, then the Christmas season would be more meaningful to us...we can celebrate the New Year any day of the month or anytime of the year, if there is a reason to celebrate."