The first shipment of U.S. supplies crossing through Russian territory is on its way to Afghanistan, the U.S. Embassy said Tuesday, as NATO scrambles to open up new supply routes for alliance forces.

The shipment most likely contained construction supplies, the embassy press office said. It refused to say when the shipment entered Russia or how far it had traveled.

The Interfax news agency, citing unnamed diplomatic sources, said the U.S. supplies had reached Russia's southern border with Kazakhstan.

Russia and several Central Asian states, including Kazakhstan, have permitted the United States and some other NATO nations to ferry non-lethal equipment by rail across their territory, thus easing a supply squeeze faced by the alliance.

NATO has been securing alternative supply routes to Afghanistan to augment the main logistical lines through Pakistan, which have come under increasing attack from Taliban guerrillas.

The supply effort took on added urgency after President Barack Obama announced that 17,000 more U.S. troops would be sent to reinforce the 56,000 allied soldiers already there.