Britain's army chief says the country's ability to withstand attack and respond to threats is being eroded by a lack of investment in the military, increasing pressure on the government to boost defense spending.

Gen. Nick Carter says in excerpts of a speech to be delivered Monday that Britain has been left exposed to adversaries such as Russia, which already boast capabilities Britain would struggle to match.

Carter says "state-based competition is now being employed in more novel and increasingly integrated ways and we must be ready to deal with them."

Following comments from other U.K. leaders about the threat posed by Russia, Carter will stress that Britain "must take notice of what is going on around us" or the country will be "massively constrained" in its ability to respond.