Prime Minister Lee Hsien Loong discussed the Russian annexation of Crimea with German Chancellor Angela Merkel on Tuesday and reiterated Singapore's opposition to such assaults on sovereignty.

During their hour-long talk, described as warm and cordial, Mr Lee underlined Singapore's objection to any "unprovoked invasion of a sovereign country under any pretext", said his press secretary Chang Li Lin.

Russia's decision to annex Crimea from Ukraine after a questionable referendum in favour of it in the peninsula has provoked the anger of western Europe and the United States, which have retaliated with sanctions.

Late on Monday here, US President Barack Obama and the other leaders also axed a G-8 meeting planned for Sochi in June, effectively kicking out Russia from the prestigious club as they revert back to a G-7 format spanning the US, Germany, Britain, France, Japan, Canada and Italy.

During his talks with the German Chancellor, Mr Lee also expressed his appreciation for her country's support for the early ratification of the European Union-Singapore FTA.

Germany is Europe's largest economy and Singapore's 13th largest trading partner, amounting to more than S$20 billion last year. Germany manufacturers in medical technology supply, aerospace, food and furniture stand to benefit from the removal of tariffs under the FTA.