A blast and gunfire, Mexico's chopper battle

A blast and gunfire rattled the hamlet in western Mexico where a drug cartel brought down a military helicopter in an intense battle that left three troops dead and three more missing.

Witnesses say around a dozen sport-utility vehicles were driving down a dirt road with their lights off early Friday while the helicopter followed closely behind in a rural area of Jalisco state.

Suddenly, people heard a "loud explosion and then you could see the bursts of gunfire," said a young woman who lives in the hamlet and declined to give her name over security concerns.

The war-like scene was the most intense fight in a spasm of violence launched by the Jalisco New Generation Drug Cartel against a military and police operation that was launched against the gang the same day.

- Rocket launcher? -

Residents and an army commander who requested anonymity told AFP the gunmen appeared to have used a weapon similar to a rocket launcher to take down the aircraft.

"The explosion produced a big black smoke cloud," another one of the Villa Vieja settlement's 60 residents said.

A federal official was unable to confirm the type of weapon used to force down the Cougar helicopter but said it was of "high-caliber, with the firepower to take down a helicopter."

On Sunday, a thin column of smoke was still billowing from a hill near the hamlet.

Of the 18 people aboard, three soldiers died and three remain unaccounted for, while 10 troops and two federal police officers were hurt.

Authorities say the helicopter came under attack after it spotted a convoy of gunmen who opened fire and hit the tail rotor, forcing it to make an emergency landing.

Officials have not said if the troops were killed by the rough landing or gunfire.

Local residents say two other helicopters were involved in a two-hour battle and shot back at the gunmen, who continued to shoot up. They fled when ground troops arrived.

- 'Highly dangerous' -

The New Generation has emerged as one of the most powerful and violent cartels in Mexico this year, attacking police forces in two ambushes that killed 20 officers in March and April.

Officials have found that the gang, led by Nemesio "El Mencho" Oseguera, builds its own assault rifles. Security experts say the cartel is well armed and coordinates its operations very well.

The helicopter attack kicked off a day of violence that included assailants burning dozens of buses, trucks, banks and gasoline stations across the state.

Four other people died on Friday, including three suspects and a state policeman.

Jalisco has become the newest challenge in President Enrique Pena Nieto's struggle to contain the country's drug cartels.

Other high-profile battlegrounds include Tamaulipas in the north and Guerrero and Michoacan in the southwest.

Pena Nieto described the gang, without naming it, as "highly dangerous" but he vowed to dismantle it.

Authorities, meanwhile, were still searching for the three missing soldiers, whose fate remained a mystery more than two days after their disappearance.

"I don't know if they're hiding, injured or kidnapped," the federal official said. "There's an intense search going on."