A spokesman for Glencore declined multiple requests for comment by American Metal Market and Metal Bulletin.

Trader sources said they have not received official confirmation of the force majeure.

Many aluminium buyers in the US market have been concerned about Glencore's ability to fulfill its contractual obligations in the wake of the US Department of the Treasury placing sanctions on Russian aluminium producer UC Rusal last week. Much of the metal received by such buyers is sourced from Russia, and from UC Rusal in particular.

As a result, market participants largely were not surprised by the force majeure reports.

“It’s not a lot of metal, I would've expected more,” one European trader said. “What you tell me is not a surprise.”

"[That canceled volume is] very small - [especially] due to the fact that, by design, they could only deliver sanctioned metal," a second European source said.

"It'll scare the consumers even more," a third European trader said.

Glencore said on Tuesday April 10 that it was evaluating its contracts with Rusal, but said those contracts were not “financially material” to the company. At the same time, Glencore chief executive officer Ivan Glasenberg resigned from his position as a director at Rusal.

In the wake of these developments, the duty-unpaid Rotterdam spot P1020 premium was said to have traded at $140 per tonne, much higher than Metal Bulletin's current assessment of $102 per tonne. American Metal Market's latest assessment of the US Midwest P1020 premium places it at 22-23 cents per lb, up more than 18% week on week.

Justin Yang, London, contributed to this report.