Yemen’s president, out of the country recuperating from wounds from an attack on his palace, still has a powerful hand on the ground at home — his son. Ahmed Ali Saleh commands Yemen’s most highly trained troops, has them deployed in the streets of the capital and seems determined to preserve his father’s rule against enormous pressure at home and abroad.

The 42-year-old Ahmed is operating from the presidential palace and his father’s main office in a military compound in the capital of Sanaa, relegating Vice President Abed Rabbo Mansour Hadi — nominally the acting president — to work from his home or his office in the Defence Ministry, several ruling party and government officials said.

The younger Saleh and his cousins have also defied pressure from the vice president to withdraw their troops from the streets of Sanaa as part of a fragile cease-fire with opposition tribesmen. In fact, since the truce began a week ago, Mr. Ahmed has brought more tanks and troops to positions in the capital’s Hassaba district near the home of the tribesmen’s leader, Sheik Sadeq al-Ahmar, a high-ranking military officer said.

“The president’s son is following a policy of escalation, as if to say he is the legitimate heir of his father,” the officer said. He and other officials spoke on condition of anonymity because of the sensitivity of the situation and for fear of retaliation from the president’s allies.

President Saleh was evacuated to Saudi Arabia last weekend for treatment after he was wounded in a June 3 blast at his palace. The hundreds of thousands of Yemenis who have been protesting against him for months and the heavily armed tribesmen who battled government troops for two weeks in Sanaa are determined to ensure that his departure means the end of his nearly 33-year-rule.

Mr. Ahmed commands the powerful Special Forces and Republican Guard. The other top internal security forces are under the command of the president’s nephews, Tareq, Yahia and Ammar. All are better trained and equipped than the regular military, parts of which have defected to join the protesters. The president’s half brother is head of the air force.

The president’s allies insist he will return soon, despite reports that Mr. Saleh, in his late 60s, was heavily burned.

“The information on the president’s health coming to the top leadership, particularly to Ahmed Ali, are reassuring, and the coming days will bring happy surprises for Saleh’s supporters,” said Yasser al-Yamani, a senior ruling party official and deputy governor of Sanaa.

The United States and Saudi Arabia are trying to convince the ruling party to move forward with a Gulf Arab-brokered deal that would end Mr. Saleh’s rule, hand power officially to his vice president, create a unity government between the ruling party and opposition and bring new elections within two months.

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