An Army paratrooper unit that led the American troop surge into Baghdad last year is returning home, marking a resumption of a troop drawdown that will test the durability of recent security gains. The drawdown began last December with the departure of one brigade, numbering about 5,000 troops, dropping the overall American troop level in Iraq to 158,000. A three-month lull was built into the drawdown plan, during which commanders saw insurgent violence shift from Baghdad to northern Iraq.

Although it has not yet been publicly announced, a senior military official told the Associated Press yesterday that the 2nd brigade, 82nd Airborne Division is heading back to Fort Bragg, N.C., in coming days and will not be replaced in the rotation. The official spoke on condition of anonymity because the movements are not completed.

That will drop the number of American combat brigades in Iraq from 19 to 18, with an additional three scheduled to leave by July. Yet to be decided is whether further reductions will be made after July; President Bush on Saturday declined to promise that he will order more cuts before he leaves office in January.

Iran vowed to push ahead with uranium enrichment yesterday, a day after the U.N. Security Council passed a third round of sanctions that Tehran called “worthless” and politically biased.

The council approved the measures in a 14–0 vote, but unity among the major powers faltered yesterday when Russia and China blocked an attempt by Western nations to introduce a resolution on Iran’s nuclear defiance at a meeting of the U.N. nuclear watchdog agency.

The dispute reflected the often contentious relations between the West and Russia and China about how to deal with Iran’s refusal to suspend enrichment and meet other Security Council demands aimed at ensuring its nuclear program isn’t trying to produce atomic weapons.

The sanctions approved Monday ordered a freeze on assets of additional Iranian officials and companies with links to the country’s nuclear and missile programs and banned for the first time trade with Iran in some goods that have both civilian and military uses.