Trump said last month he would slash the number of US troops stationed in Germany by 9,500 to 25,000, citing anger with Germany for not sticking to NATO targets on defence spending and for treating the US "badly" on trade.

The decision has caused consternation in Berlin and inside NATO over fears it could undermine the alliance's deterrence capabilities in the face of a resurgent Russia.

In a letter to 13 US Senators and Congress members, the premiers of Baden-Wuerttemberg, Bavaria, Hesse and Rhineland-Palatinate asked them "not to sever the bond of friendship but to strengthen it" by maintaining the US troop presence.

With their bases, combat units, military hospitals and other key infrastructure, the US armed forces in Germany form "the backbone of US presence in Europe and NATO's ability to act", read the letter seen by the Stuttgarter Zeitung and Stuttgarter Nachrichten newspapers.

The four regional states are all home to US military bases.

Germany hosts more US troops than any other country in Europe, a legacy of the Allied occupation after World War II.