By prodding Yemen's army to take on Islamist militants, the United States may entrench a split within its ranks and risks undermining the shaky political accord devised to stave off a descent into all-out civil war.
Four months after Washington and its Saudi-led Gulf Arab allies cajoled President Ali Abdullah Saleh into ceding power, Yemen's military command remains divided between his friends and foes. The former include a son and nephew who lead units that have received US aid to fight a Yemen-based wing of al Qaeda.
The US focus on those militants may brake a drive to restructure the military as part of a transition that sidelines Saleh and, its sponsors hope, will keep Yemen from sliding into chaos that empowers al Qaeda, some analysts and diplomats say.
Reforming the military - key to a deal Saudi Arabia brokered and America blessed to replace Saleh with his deputy - appears at most a longer-term priority for a US administration whose top negotiator with Yemen is its counter-terrorism chief.
"The deal created expectations of restructuring as a first step, a condition, for an overall political solution," said a Sanaa diplomat of the pact Saleh signed in November, intended to prevent renewed fighting between rival military units and tribal militias that followed a mass anti-Saleh uprising last year.
"But there is resistance to changing things quickly or in a single step. They (the Americans) understand this as a process which eventually reaches restructuring, so that their 'war-on-terrorism' objectives are not compromised."
Those objectives centre on al Qaeda in the Arabian Peninsula (AQAP), a force that includes members of cells who fled Saudi Arabia's 2003-2006 campaign against its own militant Islamists.
The United States accuses AQAP of plotting attacks abroad on Saudi and US targets. Last year a US drone strike killed Anwar al-Awlaki, a US citizen who American officials say directed a failed attempt to blow up a US airliner in 2009.
AL QAEDA PERIL
AQAP is seen as a potential menace to neighbouring Saudi Arabia, the world's top oil exporter, and to sea lanes off Yemen used to supply large amounts of crude to Western markets.
For the United States, a united Yemeni military, free of the divisive political in-fighting seen during the struggle to oust Saleh, is regarded as crucial to the campaign against al Qaeda.
But while the transition plan's over-arching goal is a cohesive military under professional command answering to legitimate political leaders, its terms are crucially silent on the immediate fate of individuals, notably Saleh's relatives.
Saleh had granted the United States freedom to carry out attacks on suspected al Qaeda targets in Yemen, including a 2009 missile strike in 2009 that killed dozens of civilians.
As Saleh's crackdown on protests intensified last year, his longtime ally General Ali Mohsen mutinied, taking with him the First Armoured Division, and Islamists calling themselves Ansar al-Sharia took the first of a series of towns in south Yemen.
The ease of their advance led Saleh's foes to accuse him of secretly colluding with them, the better to convince Washington of a looming al Qaeda threat which only he could help counter.
As the United States is painfully aware, such murky dealings are not new in Yemen's complex politics nor unique to Saleh.
US counter-terrorism chief John Brennan has vowed US materiel will not be used for "internal political purposes" in a land where the ex-president seems keen to retain influence.
Brennan did not refer explicitly to Saleh's son and nephew, who command units that formerly received US backing and who complained during the uprising of a decline in such aid.
"Commanders have to understand that their mission is not to fight other military commanders, it's to fight the terrorists," Brennan told reporters in Sanaa before the one-candidate vote last month that replaced Saleh with Abd-Rabbu Mansour Hadi.
"Our advice, assistance and equipment is not going to those units that are not fighting al Qaeda."
That focus on counter-terrorism may have blinded US policymakers to its effects on the political transition that they, along with the Gulf Cooperation Council (GCC), a bloc of Yemen's richer neighbours, have sponsored, some analysts say.
"NO YEMEN POLICY"
"This country (the United States) has a counter-terrorism policy and a Saudi policy, but no Yemen policy: Yemen is a theatre of counter-terrorism operations in the kingdom's backyard, not a place where a potentially democratic transition...might be occurring," said Sheila Carapico, a Yemen expert at the University of Richmond.
"This is why we sent Brennan to do a diplomat's job on the GCC plan. The American move...seems calibrated to keep the GCC happy and secure while escalating counter-terrorism in Yemen, not on any internal Yemeni dynamics," she said.
Asked for comment, a US State Department official in Washington said it was "critically important" to revamp the Yemeni armed forces if AQAP were to be neutralised.
"We are already helping the military undertake this task, but it is a difficult process that must be carefully planned.
"AQAP remains a dangerous terrorist organisation and is a significant and continuing threat to Yemen, the region, and the United States. We continue to work closely with President Hadi and the Yemeni government to confront this mutual threat."
US officials renewed such pledges of support after Hadi's inauguration, when an al Qaeda-linked group said it had carried out attacks in the south which more than 100 Yemeni troops were killed and their heavy weapons were captured.
But some Saleh loyalists read the US stance as keeping faith with military and security units where the former leader still enjoys influence that could survive any proposed shake-up.
"Whatever is done against the terrorists unites the armed forces," said Mohammed Shayaa, a retired general and director of Yemen's military academy during Saleh's rule. "As it succeeds, it restores credibility to the army."
At the time of the vote, Brennan dismissed fears Saleh would exert power behind the scenes through relatives in the military and intelligence apparatus or his political party, which under the transition plan has joined opponents in a unity government meant to stabilise Yemen before elections in two years' time.
He described Saleh, who still heads his General People's Congress party, as a "private citizen" who "has been very supportive of this political transition."
Subsequent events have seemed at odds with his view.
Officials in Hadi's office said in March that Saleh had demanded that the prime minister, Mohammed Basindwa, who represents opposition parties in the government, resign or face arrest for saying Saleh played a role in continuing violence.
They said Hadi had threatened in turn to dissolve the government, in which Saleh's party holds half the ministries, in favour of one made up solely of opposition parties.
The opposition bloc - which agreed to grant Saleh immunity from prosecution under the power transfer plan - demands he give up his party leadership and that his relatives be stripped of their commanding roles in the military and security apparatus.