BEIJING — China said Sunday that it is up to the United States to improve relations that soured over US arms sales to Taiwan and a meeting between President Barack Obama and the Dalai Lama.

Despite the tough line, Foreign Minister Yang Jiechi said China's newly assertive diplomacy is simply an attempt to safeguard its core interests and shouldn't be interpreted as combativeness.

Beijing was incensed by Washington's January announcement of a $6.4 billion weapons package for Taiwan, the self-governing island it considers Chinese territory. Beijing suspended military exchanges and has threatened to retaliate against US aerospace firms involved in the deal.

Beijing protested again when Obama met at the White House with the exiled Tibetan spiritual leader, the Dalai Lama, whom Beijing accuses of seeking independence for the Himalayan region.