Mexico's Senate demands that the government explains the murder of 15 people at a high school party in a city on the US border, despite a heavy army presence there aimed at quelling rampant drug violence.
The Senate says it will call Mexico's top anti-drug officials, including the attorney general and the defense and security ministers, to appear before lawmakers in the next few days to examine the killings, a spokesman says.
Suspected drug cartel gunmen burst into the birthday party and killed at least two adults and 13 students in Ciudad Juarez, the latest massacre in what has become one of the world's deadliest cities.
Opposition lawmakers are calling for a change of strategy in Ciudad Juarez, and Mexican President Felipe Calderon, who dispatched thousands of troops there last year to clamp down on killings, vowed on Tuesday to respond.
"The federal government will analyze extending and strengthening its strategy in Ciudad Juarez," Calderon said in a speech in Tokyo during an official visit to Japan.
He declined to give details, but signaled a bigger emphasis on social issues and not just a crackdown on crime.
More than 17,000 people have died in drug gang violence across Mexico since Calderon launched his military assault on cartels in late 2006. The escalating bloodshed is a worry for the US government, foreign investors and tourists alike.
Federal police and soldiers set up checkpoints across Ciudad Juarez and military helicopters flew overhead, but similar shows of force have failed to have an impact over the past year.
The suspected hitmen jumped out of sport utility vehicles and sprayed bullets at the teenagers, who were celebrating a classmate's birthday at a house in the city, which lies across the border from El Paso, Texas.
Patricia Gonzalez, attorney general for the state of Chihuahua that surrounds Ciudad Juarez, has said the shootings could be linked to drug cartels.
But the city's mayor Jose Reyes Ferriz told local radio that there was no motive and the shootings were random.
Some 2,650 people were killed in drug violence in Ciudad Juarez last year and cartel murders have jumped since the start of this year.
The city has become the epicenter of Mexico's increasingly violent drug war, as gangs fight over smuggling routes into the United States and access to local addicts.
Over the past two years, heavily armed hitmen have attacked each other on busy city streets and outside schools, strung murdered rivals from bridges and left severed heads outside police buildings. Killings are becoming more indiscriminate as gunmen search for rivals in parties, hospitals and drug rehabilitation centers.
Mexico is the key transit route for US-bound cocaine from South America and a top producer of marijuana and heroin.