New Delhi, July 18 -- 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.

Merz said it was "a historic day for German-British relations" as he signed an agreement that also commits the two countries to boost investment and strengthen law-enforcement cooperation against criminal people-smuggling gangs using the English Channel.

"We want to work together more closely, particularly after the United Kingdom's withdrawal from the European Union," Merz said. "It is overdue for ...