China says U.S. surveillance flights near its coast have “severely harmed” strategic trust between the countries and are a “major obstacle” to closer military ties.

The Global Times newspaper on Wednesday quoted defense ministry officials as demanding that the United States respect China's sovereignty and security interests. The remarks follow a speech this week in which U.S. military chief of staff Admiral Mike Mullen said America will “not be deterred” from flying in international air space close to China.

The Global Times article also reports that two Chinese Sukhoi-27 fighters tried to intercept a U.S. U-2 surveillance flight over the Taiwan Strait late last month. Reuters news agency says the Chinese planes briefly crossed into Taiwan's air space during the operation.

The flare-up comes amid efforts by military leaders from the two sides to mend relations after a long period of mutual distrust.

Mullen made a high-profile visit to China earlier this month, returning an earlier visit to the United States by China's military chief of staff, General Chen Bingde. Previously, contacts between the two militaries were cut off for about a year over U.S. arms sales to Taiwan.

At a joint news conference with Mullen in China, Chen pointed out that U.S. surveillance flights have come as close as 25 kilometers from China's coast. Global Times quotes a military expert as saying the flights, along with the arms sales to Taiwan, are among the biggest obstacles to closer military ties between the countries.

In his speech Monday, Mullen acknowledged the flights were a major source of disagreement between him and Chen. But he said the military leaders are trying to move past their disagreements on that and other issues.