* Explosions took place on Thursday and Friday

* Were on two different stretches of 780-km pipeline

* Pipelines usually back online within days of bombing

BOGOTA, July 5 (Reuters) - Two explosions have shut down Colombia's 80,000 barrel-per-day Cano Limon-Covenas oil pipeline, state-controlled oil company Ecopetrol said on Friday, with a military source describing them as attacks carried out by leftist rebels.

The explosions on Colombia's No. 2 pipeline, used by U.S. oil producer Occidental and owned by Ecopetrol, had no immediate impact on crude production or exports in Latin America's No. 4 oil producer, according to a media official at Ecopetrol.

No details on how much crude was spilt by the explosions or the environmental damage was immediately available, the Ecopetrol official said.

The explosions were likely carried out by a rebel group, a military source told Reuters, without attributing the attack specifically to the FARC, as the nation's biggest insurgent movement is known, or its smaller counterpart the ELN.

The guerrilla groups have attacked oil infrastructure with increasing frequency in the past year or so, even as peace talks in Cuba progress between the government and the FARC.

The Marxist FARC this week called on the government to also seek a negotiated end to its war with the ELN.

Pipelines are usually brought back on line within a matter of days after attacks, which in 2012 were as regular as one every two or three days, according to defense ministry data, almost twice as frequent as in 2011.

The first explosion on the 780-km (485 mile) pipeline happened on Thursday near El Tarra in Santander province and the second on Friday, near Saravena in Arauca province, Ecopetrol said.

The pipeline runs close to the border with Venezuela and carries crude from the Cano Limon fields to the port of Covenas on the Caribbean coast for export.

Latin America's longest-running insurgency is at its weakest in decades. But attacks on pipelines in remote areas have cut into production goals, and kept the government from reaching its target of 1 million barrels per day until late last year.

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