Jul 10, 2007
Tuesday's explosion happened near the central town of Coroneo
The Popular Revolutionary Army (EPR) said it had attacked oil installations of the state-owned oil company, Pemex.
The EPR, which has been inactive for several years, said it acted to press the government to release two of the group's jailed members.
No-one was injured in the blasts - one on Tuesday and three last week, but oil supplies were disrupted.
Mexico's government has launched investigations.
"The federal government is taking all the necessary measures to increase security around the country's strategic installation," the interior ministry said in a statement.
The EPR claimed responsibility for the blasts in a statement posted on the internet.
It said "the actions of harassment will not stop" until the release of its two jailed members.
So far there has been no independent confirmation of the authenticity of the statement.
Tuesday's explosion forced the evacuation of a number of people near the town of Coroneo in central Mexico.
It also shut down a pipeline running between Mexico City and Guadalajara.
Last week's blasts also interrupted oil supplies in Mexico, but oil exports were not affected, Pemex said.
The EPR first emerged in south-western Mexico in 1996, vowing to fight for social justice for the country's poor.