New Delhi: Opposition parties on Monday attacked the Modi government over the feud between the CBI director and his deputy, with Congress president Rahul Gandhi alleging that the probe agency was being used as a "weapon of political vendetta" under the current dispensation and was in "terminal decline".

The feud between CBI Director Alok Verma and his deputy Rakesh Asthana turned murkier with the arrest of Devender Kumar, a deputy superintendent of police in the special investigation team headed by Asthana.

The Congress said there is a serious credibility crisis in the CBI with its top officers accusing each other of massive corruption and blamed "vested interests" within the government for bringing the agency to "such a pass".

Gandhi alleged the CBI was being used as a "weapon of political vendetta" under the Modi government and that the premier investigation agency was on a terminal decline and "at war with itself".

Taking to Twitter, he cited a media report in which the Central Bureau of Investigation's second-in-command, Asthana, has been named as an accused in a bribery case. "The PM's blue-eyed boy, Gujarat cadre officer, of Godra SIT fame, infiltrated as No. 2 into the CBI, has now been caught taking bribes (sic)," Gandhi tweeted. "Under this PM, the CBI is a weapon of political vendetta. An institution in terminal decline that's at war with itself," he said.

Terming the issue "very serious", Congress leader Sachin Pilot accused the government of interference in the CBI and asked why it was silent on the issue. "How do we trust the CBI to look at corruption issues when their top people are themselves involved and allegations are flying thick and fast? The fact that it has reached this point tells you how long and how deep the rot may be within this government," Pilot told reporters at the Congress headquarters.

The CBI's top officers are accusing each other of massive corruption, he said, questioning the sanctity and the credibility of the government and the CBI to function in an "honest, unbiased transparent way". "So there are serious credibility issues and I think there are vested interests within the government and within the CBI that have brought this agency to such a pass," Pilot said.

As far as the internal functioning of the CBI is concerned, it is apparent that there is "power play and a blame game going on", he said.

Later Congress leader Anand Sharma tweeted: "Under the watch of PM Modi it is a rotten Affairs of state. CBI, ED & DRI were reduced to compliant political tools to target political opponents. Politicisation and institutional corruption is total. New twist in CBI saga finally destroys its credibility."

"Every institution including intelligence agencies have been compromised or undermined. Remember only last week all institutional sanctity was destroyed with Cabinet Secretary, Army Navy Airforce Chiefs, IB and RAW all subordinated to a political appointee NSA. A power hungry PM has inflicted a lasting damage to India's Institutions," he claimed.

The Congress has been attacking Prime Minister Narendra Modi over the appointment of Asthana as CBI special director.

In an unprecedented move, the agency has booked its special director Asthana for allegedly receiving bribes from middlemen to give relief to a businessman being probed by him in a case involving meat exporter Moin Qureshi, officials had said Sunday.

Responding to the developments, the CPI said Prime Minister Narendra Modi should clarify the situation in CBI as the credibility of the premier investigation agency is at stake.

CPI national secretary D Raja said questions are being raised over CBI's functioning after Asthana was booked by the agency last week. Asthana, too, had written about 10 cases of alleged corruption and irregularities against CBI Director Alok Verma in his letters to the Cabinet Secretary and the Central Vigilance Commission about a month ago.

Samajwadi Party spokesperson Ghanshyam Tiwari, in a tweet, said, "Governments that run like a Mafia also fight like a Mafia! Watch the #MafiaWar that BJP has led CBI into... #CBIVsCBI (sic)."