WASHINGTON- U.S. President Donald Trump said on Monday he was a "little concerned" about the $121-billion merger of defense contractor Raytheon Co and United Technologies Corp.

Trump said he thought both were great companies but worried the merger may take away competition.

"I want to see that we don't hurt our competition," Trump said in an interview with CNBC.

Later, Trump said he hoped the merger could go forward, but reiterated his concern about competition.

"I hope the Raytheon deal, I hope it can happen. But I don't want to see where we have one less person that can compete for an order. I don't want to see that. It's no good," Trump said.

Shares of both companies were higher on Monday after the surprise weekend announcement. 

United Technologies provides plane makers with electronics, communications and other equipment, while Raytheon primarily supplies the U.S. government with military aircraft and missile equipment. 

The merger, expected to close in the first half of 2020, would potentially upend the aerospace sector, creating a conglomerate spanning commercial aviation and defense procurement.

The two companies have some clients in common, but have argued business overlap is limited as they prepare to face scrutiny by U.S. antitrust regulators.

(Reporting by Doina Chiacu and Makini Brice; Editing by Chizu Nomiyama and Nick Zieminski) ((doina.chiacu@thomsonreuters.com; 202-898-8322;))