Energy stocks were lower Monday afternoon, with the NYSE Energy Sector Index falling 2% and the State Street Energy Select Sector SPDR ETF (XLE) declining 1.5%.

The Philadelphia Oil Service Sector Index was shedding 1.3%, and the Dow Jones US Utilities Index was down 1.3%.

Oil prices fell after President Donald Trump said the US and Iran were in "very deep talks," fueling optimism about the prospects of de-escalation between the two nations, though Trump also said military action could resume if diplomacy fails, according to Axios. Oman is conducting talks with Iran, but Qatar, Pakistan and Egypt are also actively involved in the process, Axios reported.

Front-month West Texas Intermediate crude oil fell 7.3% to $82.76 a barrel, and the global benchmark Brent crude contract dropped 6.2% to $86.01 a barrel. Henry Hub natural gas futures shed 3.6% to $2.77 per 1 million BTU.

In corporate news, Expand Energy (EXE) has agreed to buy private asset-backed natural gas and power marketer Twin Eagle from Five Point Infrastructure for about $1.25 billion, becoming North America's leading gas marketer. Expand Energy shares were 0.1% higher.