Turkey has asked the United States to extend the pricing on Raytheon Co’s Patriot missile defense system proposal, two sources familiar with the discussions told Reuters on Monday, a sign that Ankara is keeping its options open in case its talks with the preferred Chinese supplier fall through.

Turkish Prime Minister Recep Tayyip Erdoğan last week said Ankara would be open to new offers if its talks about co-producing a long-range air and missile defense system with China Precision Machinery Import and Export Corp (CPMIEC) fail.

Turkey’s decision to choose a $3.4 billion Chinese offer over rival bids from Russian, US and European firms has raised concern among Turkey’s Western allies.