Aden (AFP) - Yemen's embattled President Abedrabbo Mansour Hadi pledged Saturday to fight Iranian influence in his violence-wracked country after US troops at a key Yemeni airbase were pulled out.

The Americans at Al-Anad airbase have been evacuated for security reasons, a Yemeni military source there said a day after several suicide bombings at Shiite Huthi mosques claimed by the Sunni Islamic State group killed 142 people.

The troops left late Friday for an "unknown destination", the source at the base in the southern province of Lahj told AFP.

Yemen has acknowledged that American personnel gathering intelligence for drone strikes targeting Al-Qaeda are deployed at Al-Anad.

At least 29 people were killed Friday in clashes in Lahj between security forces and gunmen who included both Al-Qaeda militants and southern separatists.

Yemen is on the brink of civil war, with a deepening political impasse and an increasingly explicit territorial division along sectarian lines, amid rising violence between Huthi militia and Sunni tribes and Al-Qaeda.

Accusing the Huthis of importing Tehran's ideology, Hadi lashed out at the Iran-backed militia Saturday after the suicide bombings, which also wounded 351 people.

By claiming its first attack in Yemen, IS is seeking to exploit the chaos gripping the country where rival Al-Qaeda has traditionally been the dominant militant movement.

The Huthis, who seized Sanaa in September, vowed to take further "revolutionary steps" following Friday's blasts.

- Hadi pledge on flag -

In his first televised speech since he fled to Aden from house arrest in Huthi-held Sanaa, Hadi said he would ensure that "the Yemeni republic flag will fly on the Marran mountain in (the Huthi militia's northern stronghold) Saada, instead of the Iranian flag".

"The Iranian Twelver (Shiism) pattern that has been agreed upon between the Huthis and those who support them will not be accepted by Yemenis, whether Zaidi (Shiites) or Shafite (Sunnis)," he said.

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The Huthis belong to the Zaidi offshoot of Shiite Islam. They are believed to have converted to Twelver Shiism, which is followed by Iran, but insist that Tehran does not meddle in Yemeni affairs.

In a letter to relatives of the mosque bombings victims, Hadi condemned the attacks as "terrorist, criminal and cowardly".

"Such heinous attacks could only be done by the enemies of life," who want to drag Yemen into "chaos, violence and internal fighting", he said.

"Shiite extremism, represented by the armed Huthi militia, and Sunni extremism, represented by Al-Qaeda, are two sides of the same coin, who do not wish good and stability for Yemen and its people."

Hadi has declared Aden the country's temporary capital.

Friday's bombings came a day after clashes in the southern city between Hadi loyalists and forces allied with the Huthis.

There were signs that forces allied with the Huthis and former president Ali Abdullah Saleh were planning to seize Taez -- a strategic city between the capital and Aden.

- 'Tip of the iceberg' -

Since taking Sanaa the Huthis have tightened their grip on government institutions, aided by Saleh loyalists.

But in their push to widen their control to the south, they have faced fierce resistance from Sunni tribes allied with Al-Qaeda.

Al-Qaeda distanced itself from Friday's bombings, insisting it does not target mosques.

In an online statement claiming responsibility, the Sanaa branch of IS said the attacks were "just the tip of the iceberg".

Iran "strongly condemned" the bombings.

Mohammed Abdulsalam, spokesman for the Huthis' Ansarullah party, called the attacks part of a "clear war against the Yemeni people and its popular revolution" -- a reference to Sanaa's takeover.

He accused "Gulf-funded media" of providing political cover for Al-Qaeda in the provinces of Baida and Marib.

"It is now imperative that we complete the revolutionary steps to protect the people and their revolution," he said in a statement.

The Huthi threat came as reinforcements from the special forces, accused of links to the Huthis and Saleh, were sent to Taez, 260 kilometres (161 miles) south of Sanaa.

Military sources said some 1,200 soldiers, backed by 22 armoured vehicles, had arrived at the special forces base in Taez.

Taez is just 180 kilometres north of Aden, and seen as a strategic entry point to Hadi's refuge.

"The bombings in Sanaa will now be taken as an excuse to open new fronts by attacking Taez and Marib (in the east)," said Yemeni youth activist Bassem al-Hakimi.