UN tried desperately to enter uninvited (7)
I believe the answer is:
intrude
'enter uninvited' is the definition.
(I've seen this before)
'un tried desperately' is the wordplay.
'desperately' is an anagram indicator.
'un'+'tried'='untried'
'untried' anagrammed gives 'INTRUDE'.
'to' is the link.
(Other definitions for intrude that I've seen before include "Poke one's nose in" , "Push in unwantedly" , "Come in without invitation" , "Untried (anag)" , "Trespass" .)