Japan has sent a letter to the US expressing concern about protectionism stemming from a "Buy American" plan in Washington's mammoth stimulus package, the top government spokesman said yesterday.

The letter, sent on Wednesday to top aides of US President Barack Obama and the Senate's majority and minority leaders, echoes concerns by other US trading partners, including Canada and the EU.

"The common responsibility shared by the two countries, which are the world's No.1 and No.2 economies, is to resist protectionism together," said chief cabinet secretary Takeo Kawamura.

The letter was sent to US Secretary of State Hillary Clinton and head of the National Economic Council Lawrence Summers, as well as the Senate Majority Leader Harry Reid and Minority Leader Mitch McConnell, from Ichiro Fujisaki, the Japanese ambassador to Washington, Mr Kawamura said.

The deepening global financial crisis and the failure to complete the World Trade Organisation's long-running Doha round to free up global commerce, have raised fears that countries will block imports to protect jobs.