The United States stepped up pressure on NATO allies on Thursday to send more troops to Afghanistan to crush an expected Taliban offensive, saying the next few weeks would be pivotal in battling the insurgency, Reuters reported. Despite mounting impatience in Washington, European nations were likely to deflect the calls at the meeting of defence chiefs in the Spanish city of Seville and signs emerged of differences over tactics in what is the toughest mission in NATO's 58-year history. New U.S. and British reinforcements mean the two allies will now be providing over half of the 33,000-strong NATO Afghan force between them, with their troops located predominantly in the Taliban's southern heartlands and by the Pakistan border. "We think the upcoming spring in Afghanistan is a pivotal moment in the conflict and we're encouraging the allies to do as much as they can, as soon as they can," said a senior U.S. defence official travelling with Defense Secretary Robert Gates. "We're doing our bit," the official said. "So we'll see what the allies can do." U.S. General Bantz Craddock, who took over as NATO's Supreme Allied Commander Europe in December, will call on allies to come up with a further 2,500 troops as part of his review of the mission's needs, one alliance source said. "If we don't send more troops to Afghanistan, there is a risk we could fail," Danish Defence Minister Soeren Gade, whose country has some 390 troops mainly in the south, told reporters.