Germany's Vice Chancellor and Finance Minister Olaf Scholz said on Wednesday he was very sceptical about a request by the United States to join a military mission for the Strait of Hormuz.
The United States has proposed stepping up efforts to safeguard the sea passage in the Gulf, at a time of heightened tension between it and Iran. About a fifth of the world's oil passes through the strait.
The United States had formally asked Germany to join France and Britain in a mission to secure the strait and to "combat Iranian aggression", the U.S. embassy in Berlin said on Tuesday.
"I'm very sceptical about that, and I think that's a scepticism that many others share," Scholz told ZDF television.
Scholz said it was important to avoid a military escalation in the region and that such a mission carried the risk of being dragged into an even bigger conflict.
"That's why I think this is not a good idea," said Scholz, who is due to chair Wednesday's cabinet meeting while Chancellor Angela Merkel is away on holiday.
There is considerable opposition among Scholz's Social Democrats (SPD), junior partners in Merkel's ruling coalition, to getting involved in a U.S-led mission.
Ties between Iran and the United States have deteriorated since Washington pulled out of an international nuclear deal with Iran last year and reimposed sanctions on Tehran. Germany, France and Britain have tried to keep the deal alive.
Scholz said that Berlin still viewed the international nuclear agreement with Iran as the best option to prevent it developing a nuclear bomb.
Asked whether the coalition parties shared the same view on the U.S. request, Scholz said: "Yes, that's my impression."
Norbert Roettgen, a Merkel ally and member of her conservative bloc, said he believed Germany should not join the U.S.-led mission.
"This situation requires a European response," Roettgen, chairman of the Bundestag's foreign relations committee, told broadcaster ZDF.
"The alternative to rejecting a mission with the Americans is not to do nothing - I see that (view) among many people, unfortunately also in the SPD - but rather the alternative is a European mission, if necessary without the British, if they decide for the U.S.," he said.
Former chancellor Gerhard Schroeder, a Social Democrat, welcomed the SPD opposition to joining a U.S.-led mission.
"I very much welcome the critical remarks from the SPD. A robust U.S.-led operation could quickly escalate," Schroeder, who opposed the 2003 U.S.-led invasion of Iraq, told the Rheinische Post newspaper.
New defence minister Annegret Kramp-Karrenbauer said in a speech last week that Germany is a "reliable ally" for its NATO partners.
But she added: "We must always examine scrupulously requests for support from our partners. We mustn't affirm hastily, nor issue knee-jerk rejections." Kramp-Karrenbauer is due to meet NATO Secretary-General Jens Stoltenberg on Wednesday.