Major U.S. stock indexes were lower in afternoon trading Monday as a sell-off in some big technology and internet companies weighed down the market.

Declines in Google's parent Alphabet and Facebook depressed their sectors for much of the day, mostly offsetting gains in health care stocks, industrial companies and elsewhere. Amazon also saw a steep decline.

Alphabet tumbled as media reports suggested it faces an antitrust investigation by the Justice Department. Those reports also suggested Amazon could come under increased regulatory scrutiny. Meanwhile, the Federal Trade Commission is set to take the lead in any antitrust probe into Facebook, according to another published report.

The news helped pull technology and communications sector stocks broadly lower. Microsoft shed 2.4% and Twitter slid 4.3%. Apple dropped 0.7%, reversing an early gain, as the iPhone seller kicked off its annual software showcase .

Among the gainers, Amgen climbed 4.7% and Merck rose 2.1%. General Dynamics added 2.1%.

The indecisive trading follows the first monthly loss for the market in 2019 as investors deal with uncertainty over the U.S. and its growing use of tariffs in international trade disputes. As of Friday, the S&P 500 was down 6.6% from its record set on April 30.

Investors spent the bulk of May fleeing to safer holdings as a global trade war flared up. China and the U.S. have been escalating their trade dispute with more tariffs on each other's goods while also threatening to ban technology and resource sales. The U.S. expanded its trade war and threatened to impose tariffs on Mexican goods starting June 10 because of an immigration dispute.

All of these moves have rattled investors and their confidence in prospects for global economic growth. Bank of America Merrill Lynch lowered its earnings estimates for companies in the S&P 500, citing trade tensions. Analysts have also warned that uncertainty over trade deals will crimp business confidence and keep companies from investing internationally.

KEEPING SCORE: The S&P 500 index was down 0.2% as of 2:20 p.m. Eastern time. The Dow Jones Industrial Average added 25 points, or 0.1%, to 24,840. The technology-heavy Nasdaq composite fell 1.3%. The Russell 2000 index of small companies added 0.5%.

Major stock indexes in Europe were broadly higher.

DEAL OR NO DEAL: News of deals, made and denied, drove movement for several stocks early Monday.

Cypress Semiconductor surged 24.4% on the announcement that German chipmaker Infineon is buying the company for more than $10 billion in cash. Cypress Semiconductors specializes in wireless and USB technology and Infineon said the deal with create the eighth biggest chipmaker in the world and a leading supplier of chips to the automotive sector.

Centene slid 8.2% after Humana declined to make a buyout proposal. Both insurance companies focus heavily on government-sponsored plans, including Medicare and Medicaid. Humana made clear that it is not seeking Centene in a rare filing aimed at quashing investor speculation. Humana shares rose 2.3%.

El Paso Electric jumped 13.5% after getting a $2.78 billion buyout offer from a private equity fund affiliated with J.P. Morgan.

ANXIETY PUSHES DEFENSE: The U.S. decision to expand its trade war beyond China is adding to fears that economic growth and corporate profit growth will take a hit this year.

"Things are likely to get worse before they get better," said a Bank of America Merrill Lynch report.

The investment bank is recommending more caution from investors as trade disputes play out. Investors have already been heading to less-risky holdings, including utility stocks and bonds, since the trade dispute with China sharply escalated in May.

Companies in the S&P 500 performed better than expected in the first quarter, posting less than a half-percentage point contraction in profit, according to Factset. But, the trade war continues hanging over the current quarter, with analysts expecting a 2% contraction in corporate profit.

INTERNET INVESTIGATIONS?: Alphabet, the parent company behind search engine Google, dropped 6.5% following media reports that it could face an antitrust investigation by the Department of Justice.

The company has faced a series of European regulatory investigations into its practices. In one instance last year, it was fined $5 billion by European regulators over contracts dealing with smartphone makers and the search engine's apps.

The speculation over the latest investigation comes on top of a tough weekend for the company when high levels of network congestion caused user outages in some of its services, including YouTube and Google Cloud.

Meanwhile, Amazon and Facebook could face scrutiny from the Federal Trade Commission. Reports say consumer groups and vendors have complained that Amazon is unfairly edging out competition as it expands its business and offerings. The stock lost 4.4%.

The Wall Street Journal, citing unnamed sources, reported Monday that the FTC is in position to lead a possible probe into whether Facebook has become a monopoly. Shares of the social media giant plunged 7.3%.