Bratislava  - A high-level US Defence Department official told a conference Thursday in the capital of relatively new NATO member Slovakia that credible backing for the alliance's joint- defence clause is a White House priority and that it will require a more efficient organization.

"President (Barack) Obama was quite clear when he said that if (the NATO charter's) Article 5 is to be credible, it has to backed up by the appropriate contingency planning and - one could add - a credible program of exercises to show that the plans are feasible and can be implemented when they have to be," said Alexander Vershbow, US assistant secretary of defence.

Vershbow was speaking at a forum accompanying a ministerial meeting of the North Atlantic Treaty Organization (NATO).

Article 5 is a commitment by NATO members to consider an attack against one member an attack against them all.

Vershbow made reference to last year's conflict in August between Russia and Georgia, which aroused concerns about the potential threat from Moscow to former Soviet and East bloc states.

"The bottom line for me and my government is that this is an important priority, made all the more urgent in the wake of the anxieties aroused by August 2008, and we want to see that the Article 5 guarantee is meaningful for all members of the alliance," Versbow added. "NATO has to fulfill its pledges if it wants to remain relevant in the future."

Vershbow said that because the alliance is now defending a greater area than ever before, "an increasing focus on deployable capability packages" is necessary. This view was echoed later Thursday by NATO Secretary General Anders Fogh Rasmussen, who said that a credible territorial defence, which he called a NATO priority, required greater mobility and flexibility.

"If (military forces) are not flexible, we need transformation in the sense of more flexibility and deployability," Rasmussen said.

Slovakia, once a part of Czechoslovakia, gained NATO and European Union membership in 2004. It adopted the euro earlier this year.(dpa)