Barack Obama's steely vow to hunt down all those responsible for the attempted bombing of an American airliner on Christmas Day has left a crucial question unanswered: whether it was his personal order to US military forces to attack two suspected al-Qaida bases in Yemen with cruise missiles on 17 December that triggered a "revenge" terrorist operation against the Northwest Airlines plane one week later.

According to a report aired on 18 December by the American ABC News network and not denied by the White House, US and Yemeni government forces jointly targeted al-Qaida training camps in the Arhab district, 60km north-east of the capital, Sana'a on 17 December. Another alleged camp in the village of al-Maajala, in Abyan, 480km south-east of Sana'a, was also hit after US officials determined "an imminent attack against a US asset was being planned" there.

Both targets were bombed repeatedly from the air by Yemeni air force planes. Subsequent official estimates said about 35 militants were killed. But Yemeni opposition spokesmen said a total of between 60 and 120 people had died during bombardments of the two targets and a third location. They said many of those killed were civilians, including women and children. They denied the villages contained al-Qaida camps.

Television pictures broadcast from Yemen by the Arab news channel al-Jazeera on 18 December showed dozens of bodies covered in sheets.

Citing unidentified administration sources, ABC News reporter Brian Ross said the US military fired two cruise missiles during the attacks, one at each alleged camp, after Obama personally gave the go-ahead. "White House officials tell ABC News the orders for the US military to attack the suspected al-Qaida sites in Yemen on Thursday came directly from the Oval Office," Ross reported.

American officials have neither confirmed nor denied a US role in the air strikes, while the Yemeni government has insisted only its own forces were involved. "We are not going to get into any details at this point," one US official said. The official added that Yemen and the US "co-operate closely on counter-terrorism".

But White House officials could confirm that Obama telephoned Yemen's, Ali Abdallah Salih, after the raids to "congratulate" him on his efforts to combat al-Qaida.

Asked about a New York Times report on 19 December of US involvement in the attacks, Bryan Whitman, a Pentagon spokesman, said: "Yemen should be congratulated for actions against al-Qaida." The newspaper said Obama had approved US military and intelligence support, following a request from the Yemeni government. The assistance was intended to help stem growing attacks against American and other foreign targets in Yemen.

According to an Associated Press report, also published on 19 December, residents of Abyan said there was no al-Qaida training camp in the area and that the air attack had destroyed homes – a collection of mud brick houses, huts and tents – in the rural tribal area. The report said a mass grave had been dug for those killed.

Obama's actions in supporting the Yemen attacks appear to have had a bigger than expected impact. In a statement issued on Monday claiming responsibility for organising the failed bombing of Northwest Airlines flight 253, al-Qaida said the plot was specifically intended to avenge US attacks on the group in Yemen and "unjust aggression on the Arabian peninsula".

"From here, we say to the American people: since you support your leaders and you stand behind them in killing our women and our children, rejoice for what will do you harm. We have come to you with slaughter and we have prepared for you men who love death as you love life," that statement said.

The US military's support for the Yemeni operations marks a significant escalation in US involvement there and may presage a deepening intervention in coming months as Obama follows up on his vow to track down the would-be bombers. Speaking on Fox News on Sunday, Senator Joe Lieberman called for immediate, extended "pre-emptive" military action in Yemen to counter the terror threat.

Obama has taken a close interest in combating the al-Qaida build-up in Yemen since taking office in January. He sent his senior counter-terrorism adviser, John Brennan, to Sana'a in September and issued a statement proclaiming Yemen's security to be "vital" to the US national security interest.

Last month Yemen announced it had signed a military co-operation pact with the US, although Washington was unforthcoming about the details. Yemen's official Saba news agency said the co-operation agreement was signed during talks in Sana'a between the two countries' militaries.

Now, having taken the plunge, Obama faces the prospect of the opening up of another front in the "war on terror" as jihadis displaced by US military action in Afghanistan and Pakistan make the trek south – and attempt to turn the Arabian peninsula into a new launch-pad for attacks against the west.