President Donald Trump on Monday prodded the Republican-led U.S. Congress to pass major health care legislation but huge obstacles remained, with a senior lawmaker saying the Senate was unlikely to take up the stalled bill until next week.

The House of Representatives approved its health care bill in May but the Senate's version appeared to be in growing trouble as lawmakers returned to Washington from a week-long recess.

"I cannot imagine that Congress would dare to leave Washington without a beautiful new HealthCare bill fully approved and ready to go!" Trump wrote on Twitter, referring to the seven-year Republican quest to dismantle Democratic former President Barack Obama's signature legislative achievement.