Four large blasts rocked Kenya’s Westgate Mall on Monday, sending large plumes of smoke over an upscale suburb as Kenyan military forces sought to rescue an unknown number of hostages held by al-Qaida-linked militants.

The explosions were followed by volleys of gunfire, then a thick, dark column of smoke. Military and police helicopters and one plane circled over the Nairobi mall, giving the upscale Westlands neighborhood the feel of a war zone.

Security forces’ efforts the previous day to rescue the unknown number of hostages inside failed despite the military announcing that “most” hostages had been saved.

Kenyan officials have said preserving the hostages’ lives is a top priority, greatly complicating the rescue effort.

Kenyans and foreigners were among the 68 persons confirmed dead by the country’s Red Cross, including British, French, Canadians, Indians, a Ghanaian, a South African and a Chinese woman. The UK Foreign Office said Monday it has confirmed the deaths of four British nationals.

Two al-Shabab fighters have also been killed in the ongoing military raid to end the standoff and more than 175 people were injured, including many children, Kenyan officials said.

From neighboring Somalia, Sheik Ali Mohamud Rage, spokesman for al-Shabab, the militant group that claimed responsibility for the attack, said in an audio file posted on a website that the hostage takers had been ordered to “take punitive action against the hostages” if force was used to try to rescue them.

Military helicopters circled over the mall at daybreak Monday, when about five minutes of sustained gunfire broke out inside the mall, a clear indication that at least one of the estimated 10 to 15 gunmen who attacked the mall when it was filled with shoppers Saturday was still on the loose. A military ambulance then sped away from the scene.

A person with knowledge of the rescue operation told AP that no hostages had been released or rescued overnight Sunday. The person insisted on anonymity in order to talk about the rescue response.

At the Oshwal Centre next to the mall, the Red Cross was using a squat concrete structure that houses a Hindu temple as a triage center. Medical workers attended to at least two wounded Kenyan soldiers there on Monday.

Al-Shabab militants reacted angrily on Sunday to the helicopters hovering over the mall, and warned on Twitter that the Kenyan military action was endangering hostages.

A large military assault began on the mall shortly before sundown on Sunday, with one helicopter skimming very close to the roof of the shopping complex as a loud explosion rang out, far larger than any previous grenade blast or gunfire volley.

As the crisis surpassed the 48-hour mark, video taken by someone inside the mall’s main department store when the assault began emerged. The video showed frightened and unsure shoppers crouching and loud volleys of gunfire could be heard.

The terrorists stormed the mall on Saturday from two sides, throwing grenades and firing on civilians.

Kenya’s Cabinet Secretary for Interior, Ole Lenku, told a news conference on Monday:
“We don’t want to give you a definitive position on when we think the process will come to an end, but we are doing anything reasonably possible, cautiously though, to bring this process to an end”.

Al-Shabab said the attack, targeting non-Muslims, was in retribution for Kenyan forces’ 2011 push into neighboring Somalia.