WASHINGTON, March 25-- U.S. State Department confirmed on Wednesday that Yemen's President Abd-Rabbu Mansour Hadi "is no longer at his residence" in the southern Yemeni city of Aden, and said the U.S. was in touch with him earlier in the day.

"We had been in touch as recently as this morning," State Department spokeswoman Jen Psaki told reporters. "I am not in a position to confirm any additional details from here about his location."

"In terms of his departure, I think it's pretty clear he left voluntarily. I don't think I need to put a new characterization on it," the spokeswoman said.

A source at the Yemeni presidential office told Xinhua that Hadi remained in Aden Wednesday to command his forces to fight against the Houthi group following the defeat of his tribal militia in the southern province of Lahj.

The Shiite Houthi fighters backed by security forces advanced in Yemen's south and took control of a strategic military air base in Lahj early on Wednesday, a military official said.

They are advancing into Lahj's central regions, about 50 km away from Aden province where Hadi stays, the official added.

A senior Houthi member told Xinhua that the group has arrested in Lahj province Defense Minister Major General Mahmoud al-Subaihi, who has been commanding most of the pro-Hadi army to battle the Houthis.

The White House "strongly" condemned the recent offensive military actions undertaken in Yemen that have targeted Hadi.

"The actions of the Houthis and former President (Ali Abdullah) Saleh have caused widespread instability and chaos that threatens the well-being of all Yemenis," White House spokesman Josh Earnest told reporters on Wednesday.

The U.S. called on Houthi forces to stop fomenting instability and violence, and cooperate with UN-led process to resolve the differences among all sides, Earnest added.