Sentence:  It [Europe] now pressed Washington to begin direct talks with Tehran, but Undersecretary of State Nicholas Burns, Rice's point man on Iran, still stressed that diplomatic <WSD>isolation</WSD> of Iran—and not diplomatic engagement—was the only acceptable approach for dealing with the Iranian nuclear challenge. 
Meaning of the word marked with <WSD> tags:  The state of not having diplomatic relations with other countries (either with most or all other countries, or with specified other countries).