The United Kingdom, France and Germany have agreed to restore tough U.N. sanctions on Iran by the end of August if there has been no concrete progress on a nuclear deal.

LONDON — U.K. Prime Minister Keir Starmer and German Chancellor Friedrich Merz signed a landmark treaty on Thursday that pledges to tighten defense ties, as European nations try to protect Ukraine, and themselves, from an aggressive Russia in the face of wavering support from President Donald Trump’s U.S.-focused administration.