 -- A manhunt is underway in Turkey after a gunman went on a rampage in a crowded Istanbul nightclub during New Year's Eve celebrations early Sunday morning, killed at least 39 people and injured at least 69 more, according to Turkish Interior Minister Suleyman Soylu.

The popular Reina club had attracted a diverse crowd of between 400 and 500 patrons from foreign countries as well as Turkey to ring in the new year before the attack by an apparently lone shooter at around 1:15 a.m, authorities said.

Turkish police said one gunman perpetrated the violence. Later, they released on social media photos of men whom they said were the Istanbul nightclub "attackers," images which they said were of the men going through a passport check-in as they entered Turkey.

The gunman armed with what authorities described as a long-barreled weapon killed a policeman and a civilian outside of the club before "[raining] bullets in a very cruel and merciless way on innocent people" inside the club, according to Visip Sahin, the governor of Istanbul.

Twenty-four of the 39 killed were foreign nationals, according to Turkey's state-run news agency. Authorities said the foreign victims hailed from Belgium, France, India, Israel, Jordan, Lebanon, Saudi Arabia and Tunisia.

Among the nearly 70 people injured was a small business owner from Greenville, Delaware, Jake Raak, who was shot in the leg, family members told ABC station WPVI-TV in Philadelphia. Raak's brother, Michael, told WPVI-TV the bullet may have struck his cellphone, which prevent him from being injured more seriously.

The U.S. is not aware of any Americans dying in the attack, the U.S. State Department said early Sunday.

Of the 69 people who were injured, four were hospitalized in serious condition, according to Soylu, who described the attack as "inhuman."

"This was a massacre, a truly inhuman savagery," Soylu said.

At a press conference Sunday, Soylu said the assailant arrived wearing a jacket and pants, and is believed to have left wearing different clothing.

Turkish President Recep Tayyip Erdogan said in a statement Sunday, "I vehemently condemn the terror attack ... Turkey continues its combat against terror and is absolutely determined to do whatever is necessary in the region to ensure its citizens' safety and peace."

The U.S. issued a statement offering assistance to Turkish authorities.

"The president was briefed by his National Security Team on the attack in Istanbul," President Obama's principal deputy press secretary Eric Schultz said in a statement. "The president expressed condolences for the innocent lives lost, directed his team to offer appropriate assistance to the Turkish authorities, as necessary, and keep him updated as warranted."

Mark Toner, America's State Department's deputy spokesman said in a statement, "The United States strongly condemns the terrorist attack on a nightclub in Istanbul, Turkey ... We will remain in close touch with Turkish authorities throughout the investigation ... We stand in solidarity with our NATO Ally Turkey in combating the ongoing threat of terrorism."

Russian President Vladimir Putin, whose complex relationship with Turkey was further complicated in December after a Russian ambassador to Turkey was shot dead today by a lone gunman fired at him at a photo exhibition in Ankara, Turkey's capital in a widely-seen, on-camera attack, sent Erdogan a telegram of condolences, according to the Kremlin, writing, "It is hard to imagine a more cynical crime than killing innocent people during New Year celebrations. However, terrorists don't share moral values. Our common duty is to combat terrorists' aggression," Putin said.

Turkey has suffered numerous terrorist attacks in recent years, including bombings.

Among the incidents in the country were a suicide attack at a wedding this August and coordinated shootings and bombings of Istanbul's major international airport in June, attacks that killed scores of civilians.

ABC News' Darren Reynolds, Devin Villacis, Engin Bas, Benjamin Gittleson, Troy McMullen and the Associated Press contributed to this report.