WASHINGTON - The United States was "very concerned" about developments in Egypt's political turmoil, the State Department said on Wednesday, blaming the embattled President Mohamed Morsi for not doing enough to steer his country out of the current crisis.

"We do, of course, remain very concerned about what we're seeing on the ground," department spokeswoman Jen Psaki told reporters at a regular press briefing. "And we do realize, of course, that is an extremely tense and fast-moving situation in Egypt."

Latest reports said the army has replaced the president with the head of the Supreme Constitutional Court to run the country for a transitional period and suspended the constitution backed by Morsi's supporters.

Psaki said Morsi's speech made on Tuesday night lacked " significant steps" to resolve Egypt's worst crisis since the 2011 revolution that overthrew Hosni Mubarak.

"We have said that he must do more to be truly responsive and representative to the justified concern expressed by the Egyptian people," Psaki said. "And unfortunately, that was not a part of what he talked about in his speech."

Morsi, the first elected president of Egypt, rejected calls for his resignation or early elections.

In a phone call to Morsi on Monday while on a trip in Africa, US President Barack Obama encouraged his Egyptian counterpart to respond to concerns voiced by the protesters across the country, stressing that the current crisis can only be resolved through a political process.

Psaki said "we believe all sides need to take steps to talk with each other, to engage with each other, to lower the level of violence and call for an end to the violence."

Supporters of Morsi have been engaged in confrontations with opponents of the president's policies for the past year since he took office, resulting in dozens of deaths across the country in the past few days.