It is saddening to see that relations between the two countries should have deteriorated to the present state.

两国关系恶化到今天这个地步，是令人痛心的。

《新英汉大辞典》

Relations between the two countries, often uneasy, have deteriorated.

两国之间常常不稳定的双边关系已经恶化。

youdao

The test, if it goes ahead, will also roughly coincide with an annual joint military exercise between America and South Korea, at a time when relations between South and North have deteriorated badly.

如果付诸实施，那么这次试射也将在一个南北关系严重恶化的时期，与美韩年度联合军事演习的日期大致重合。

youdao

Eritrea's relations with the international community have deteriorated in recent years amid President Isaias Afwerki's refusal to cooperate in a border dispute with Ethiopia.

VOA: standard.2009.03.23

Israel and Turkey were until recently close allies both on a military and political level, but since the Israeli attack on Gaza last year, relations have rapidly deteriorated.

VOA: standard.2010.06.01

Relations between the two Koreas have deteriorated steadily since the Cheonan, a South Korean naval vessel in the Yellow Sea, exploded a month ago, killing 46 crew members.

VOA: standard.2010.05.26

Relations deteriorated after Delhi said gunmen involved in last November's Mumbai attacks were from Pakistan.

BBC: India and Pakistan discuss terror

Turkey was Israel's closest Muslim ally but relations have deteriorated over the past few years.

BBC: Deaths as Israeli forces storm Gaza aid ship

Relations between the sides deteriorated so sharply that there were fears that a fledgling peace process under way since February last year could unravel.

BBC: Kashmir border: India kills Pakistani soldier