Defence Secretary Michael Fallon sought to dispel US concerns about cuts in his country's defences, saying it was maintaining and developing a credible capability and urging fellow European Nato members to step up their forces.
Last week US Army Chief of Staff General Raymond Odierno caused a stir in London when he questioned Britain's plans and urged London to maintain spending at the North Atlantic Treaty Organization's agreed level of 2% of national output into the future.
Odierno, in an interview with the Daily Telegraph newspaper, warned that with its force cuts British units could end up fighting inside US units rather than alongside them.
Britain reduced defence spending by about 8% in real terms in the last four years to help cut a record budget deficit, shrinking the size of the armed forces by around one sixth.
Speaking during a joint news conference at the Pentagon, Fallon said his government had committed to maintaining the 2% level this year and next. Future plans would depend on later reviews, he said, but he insisted Britain's capabilities were adequate.
"Let me make it very clear, that we are meeting the 2% target this financial year, we are going to be meeting it next year" Fallon said.
Britain and the United States, two of the main pillars of the Nato alliance, have a long history of close military cooperation, including most recently in Afghanistan and in the campaign against Islamic State in Iraq.
Secretary Carter said he appreciates the independence of the alliance of the UK partnership.
"One of the things that we have valued for a long time in the UK military is the ability to act independently, to be a force of its own in the world.
"We need that because we need as many kindred countries in the world as we can who are capable of wielding their own influence independently of us" Carter said.
The Defence Chiefs also warned Russia that continued disregard for destabilizing activity in Ukraine would lead to additional sanctions.
"The United States has been clear from the outset of the crisis in Ukraine that we support the sovereignty and territorial integrity of Ukraine.
"And we've been very clear that if Russia continues to flout the commitment it made in September and February in the Minsk Agreements, the cost to Russia will continue to rise, including and especially through sanctions in coordination with our European allies and partners" Carter told reporters.
The United States recently placed sanctions on eight Ukrainian separatists and a Russian bank, warning that recent attacks by rebels armed by Russia violated a European-brokered ceasefire in the war-torn country.
The sanctions signal Washington is ratcheting up pressure on Moscow a day after accusing Russia of sending tanks and heavy military equipment into Ukraine, which is a breach of the Minsk accord agreed on 12 February.