British Prime Minister Gordon Brown said Wednesday that NATO nations are ready to offer about 5,000 more troops for the war in Afghanistan.
Lewis said Brown has written to NATO Secretary-General Anders Fogh Rasmussen to update him.
Britain has not named the countries it claims will provide the extra troops, though Slovakia last week offered 250 more soldiers following London talks. Georgia has pledged between 700 and 1,000 soldiers, and South Korea has said it would send "several hundred" to protect its reconstruction teams.
Brown plans to send 500 more British troops — not included in the 5,000 figure — soon after President Barack Obama announces his plans for reinforcements. The U.K. currently has 9,000 troops in Afghanistan.
In Brussels, NATO spokesman James Appathurai said some allies plan to delay their decisions on further troop pledges until after an international conference on the future of Afghanistan, tentatively scheduled for January.
"Nobody should expect that the day after President Obama makes his announcement that there will be a total troop figure added up ... by the other allies," Appathurai said.
"A number of countries ... are looking to that conference," he said. "They want to see any further contributions in the context of the overall political environment in which they will be deploying their forces."
Committing additional troops for Afghanistan will be a tough sell for many allied governments at a time of economic crisis and shrinking defense budgets. Polls show that most Europeans oppose sending more soldiers into what many see as an unwinnable conflict.
The Canadians and the Dutch are both scheduled to begin pulling troops, even as Obama considers pouring them in.