WASHINGTON — Facebook and Twitter executives pledged on Wednesday to better protect their social media platforms in the 2018 elections and beyond, and told Congress of aggressive efforts to root out foreign intrusions aimed at sowing divisions in American democracy.

Facebook’s No. 2 executive, Sheryl Sandberg, and Twitter’s CEO, Jack Dorsey, testified before the Senate intelligence committee, but there was an empty chair for Google’s parent Alphabet, which refused to send its top executive.

Senators had sharp words for Alphabet CEO Larry Page, who oversees Google. Sen. Marco Rubio, R-Fla., suggested the company might have bailed because it was “arrogant” while Sen. Susan Collins, R-Maine, expressed outrage over the absence.

Sandberg’s appearance came several months after Facebook CEO Mark Zuckerberg testified in highly publicized Capitol Hill hearings. Like Zuckerberg, she acknowledged Facebook’s lag in recognizing Russian efforts to manipulate Facebook during and after the 2016 U.S. presidential election. Sandberg detailed Facebook’s efforts to fight the problem with new technologies and manpower.

“We are even more determined than our adversaries, and we will continue to fight back,” Sandberg said.