Venezuela’s state-run oil company Petroleos de Venezuela (PDVSA) said a recent cyberattack has impacted its administrative system.

PDVSA published a statement on Monday that confirmed the attack but claimed the company has still been able to operate. The statement blames the cyberattack on the United States — which has increased its military presence around Venezuela in an effort to remove current president Nicolás Maduro. 

“This attempt at aggression adds to the public strategy of the U.S. government to take over Venezuelan oil by force and piracy,” the company said. “Petroleos de Venezuela, S.A. categorically rejects this despicable action, orchestrated by foreign interests in complicity with stateless actors that seek to break the country's right to its sovereign energy development.”

Aside from PDVSA’s accusations, cybersecurity experts have not found evidence linking the attack to the U.S. government.

Reuters spoke to four sources who said the cyberattack was more damaging than PDVSA is portraying. The company’s website is down as of Tuesday afternoon and Reuters said oil cargo deliveries were suspended as a result of the cyberattack. 

"There's no delivery (of cargoes), all systems are down," one company source told Reuters, adding that workers are calling it a ransomware attack.

The cyberattack comes one week after the U.S. military took the extraordinary step of seizing a PDVSA tanker carrying nearly two million barrels of Venezuelan crude oil. The seizure drew condemnation from the Cuban government and tankers headed for Venezuela have turned around out of fear over U.S. military action. 

According to documents obtained from the company by The New York Times, PDVSA is a key cog in Venezuela’s financial ties to China, Russia, Iran and Cuba.

The U.S. has accused Venezuela’s government of supporting narcotics traffickers and has clashed with Maduro’s regime by conducting air strikes on boats near the country’s coast. Maduro, widely considered to be a dictator after claiming wins in two disputed elections, has been accused of electoral fraud, human rights abuses and implementing policies that have cratered the country's economy.

Venezuela’s government accuses the U.S. of wanting to take over the country to gain access to its oil reserves. 

“This action is part of the U.S. escalation aimed at hampering Venezuela’s legitimate right to freely use and trade its natural resources with other nations, including the supplies of hydrocarbons to Cuba,” a Venezuelan government official said in a statement following the tanker seizure. 

U.S. officials said this week that they are likely to seize more tankers in the coming weeks.