diplomatic channels

基本解释

A: We have noted relevant report and expressed concern to the ROK through diplomatic channels.
答：我们注意到了有关报道，并已通过外交渠道向韩方表明关切。
www.fmprc.gov.cn
The United States has no formal diplomatic presence in North Korea. However, Washington says it is using diplomatic channels to seek the reporters' release.
美国在北韩没有正式外交机构，不过华盛顿表示正在通过外交途径争取两名记者获释。
The Chinese side accepted the invitations with appreciation. The dates of the visits will be settled through diplomatic channels.
中方接受邀请并对此表示感谢，具体访问日期将通过外交渠道另行商定。
www.fmprc.gov.cn

And I think he realizes that the only way to resolve this really is through diplomatic channels.
NPR: Iran, Britain at Impasse over Captives
In a gesture this week, the Egyptian government cut government-to-government contacts with Israel, though diplomatic channels remain open.
ECONOMIST: But there is little they can do