Nato Secretary-General Jens Stoltenberg said on Thursday he believed the bond between the United States and Europe would survive any differences over trade, climate or the Iran nuclear deal.
His remarks come before a Nato summit in Brussels next month which will take place against a backdrop of tension over US President Donald Trump's policies on trade, foreign affairs, and his past criticism of the defence alliance.
“Our bond is strong but some are doubting the strength of that bond,” Mr Stoltenberg said in a speech in London. And, yes, we see differences between the United States and other allies over issues such as trade, climate and the Iran nuclear deal.
“It is not written in stone that the transatlantic bond will survive forever but I believe we will preserve it.”
He said he expected Mr Trump to be “very strong” on defence at the summit - a reference to the US president’s complaint that fellow Nato members were not honouring a commitment to try to raise defence spending to two percent of national output.
Mathieu Boulègue, a Russia researcher at international thinktank Chatham House, said: “Trump is more responsible for these cracks [within Nato] than the USA.
“Trump is personally invested in the two per cent issue; he is highly fixated on it, it’s his own, personal business-minded approach: take it or leave it.”
Mr Stoltenberg met Mr Trump earlier this year and praised his work to push Nato members into meeting the commitment. On Thursday, he took a conciliatory tone, saying it was also necessary to recognise that European states had started to increase their spending.
“It is possible to say we have done a lot, but a lot remains,” he added.
Mr Stoltenberg praised Britain for being one of the countries to meet the spending target, saying the alliance relied on all the defence capabilities Britain had.
Mr Stoltenberg’s visit to the UK came as the Financial Times reported that British Prime Minister Theresa May had questioned the country's status as a “tier one” military power. Mrs May's office denied the report and said Britain was committed to maintaining its current status.