WTO chief Pascal Lamy has said in Geneva that Washington's move to hike tariffs on Chinese-made tyres was a matter of concern that could increase the risk of a tit-for-tat spillover. br/br/The United States last week imposed punitive tariffs of 35 percent on Chinese-made tyre imports a move that prompted Beijing to lodge a complaint this week at the World Trade Organization. br/br/Beijing charges that Washington's move violates WTO rules but US President Barack Obama has denied that it amounted to protectionism.br/br/Obama and his Chinese counterpart Hu Jintao pledged to resist protectionism during a meeting in April. The Group of 20 top developed and developing countries have also made a similar pledge.