The UK should follow the lead of "competitor nations" such as France and Japan and appoint an ambassador, he said.
"The U.S. president cannot appoint an ambassador, he cannot even solely decide on the sale of a helicopter," he said last year.
The administration has promised to remove Sudan from the list of state sponsors of terrorism, to appoint an ambassador and to consider debt relief and other measures following the independence of southern Sudan in July.
He has not sat down with the loudest critics of Cuba, who have blocked US efforts to roll back trade restrictions and appoint an ambassador to represent the interests of the US in Havana.
China's announcement that it would reopen its embassy in the country comes less than a month after the US said it would appoint an ambassador to Mogadishu for the first time since closing its headquarters there 23 years ago.
The Obama administration should quickly appoint an ambassador to Turkmenistan — the position is vacant for over two years — and an invitation to the White House for President Gurbanguly Berdymukhammedov may be in order.
