UPDATE 1-'We need Turkey to buy the Patriot' missile defense system -acting Pentagon chief

Acting U.S. Defense Secretary Patrick Shanahan said on Tuesday he wants Turkey to remain in the F-35 fighter jet program, but added that Ankara needed to buy the Patriot missile defense system as Washington looks to increase pressure on its NATO ally to drop the purchase of Russia's S-400 defense system.

The United States is expected to make a decision soon on a years-long standoff with Turkey after failing to sway President Tayyip Erdogan that buying the Russian air defense system would compromise the security of F-35 stealth aircraft. At a House of Representatives Armed Services Committee hearing, Shanahan was asked whether the United States wanted Turkey in the F-35 program.

"We absolutely do; we need Turkey to buy the Patriot," he answered. Washington has opposed Turkey's plans to buy Russia's S-400 air defense system, on concerns that would compromise the Lockheed Martin Corp-made F-35's security.

In the strongest signal yet from Washington that Ankara cannot have both the advanced aircraft and the S-400, officials have told Reuters the United States could soon freeze preparations for delivering the F-35 to Turkey. The Patriot system is made by Raytheon Co.

Although Turkey has held out the prospect of buying both the S-400 and the Patriot system, the United States has warned Turkey it will take its offer of Patriots off the table unless it changes course. On Sunday, Erdogan said Turkey will not go back on the purchase of the S-400 systems from Russia, regardless of what the United States says.

The strains on ties between Washington and Ankara already extend beyond the F-35 and include strategy in Syria, Iran sanctions and the detention of U.S. consular staff. (Reporting by Idrees Ali; editing by Jonathan Oatis and Dan Grebler)