The Enforcement Directorate on Thursday questioned Congress chief Sonia Gandhi for over two hours in a money laundering case related to the National Herald newspaper.
The day was a show of strength for the party with street protests and leaders courting arrest across the country.
She has been summoned again on July 25.
Thursday's session of questioning the 75-year-old, who is recovering from Covid, ended on her request after two hours and 15 minutes, officials said.
However, Congress leader Jairam Ramesh said the ED told Sonia Gandhi that they had no further questions and she could leave.
Gandhi said she would be willing to respond to any other questions they might have and was ready to stay on till 8 pm or 9 pm if necessary, Ramesh tweeted.
She also said she was a Covid patient and needed to take her medicines so she should be informed about what time she should appear next.
Gandhi replied to about 27 top 28 questions on Thursday.
Following this, she told the officials that she needs to take her medicines at home owing to her recent Covid recovery and the agency allowed ending the day's session.
According to sources, while the Congress chief was leaving, the ED asked her to depose on July 26 but she suggested that she can come on July 25, to which both sides agreed.
"The agency wants to take its probe forward in the best way possible and we do not want her to feel uncomfortable given her age and recent health issues," an ED official said.
According to Ramesh, the ED said it had nothing to ask of her either Thursday or Friday.
After which Sonia Gandhi said she was willing to appear on Monday, Ramesh added.
The questioning was conducted keeping in mind Covid protocol with everyone participating equipped with a Covid-negative certificate.
An ambulance and two doctors from All India Institute of Medical Sciences were also stationed inside the ED office premises.
Sonia Gandhi was questioned by the same assistant director-level investigation officer who interrogated her son Rahul Gandhi in the case related to alleged financial irregularities in the Congress-promoted Young Indian Private Limited, which owns National Herald.
A woman officer was part of the questioning team.
The questioning began around 12.30 pm. Sonia Gandhi left the ED office along with her daughter around 2.30 pm.
It is understood that Sonia Gandhi has been responding to ED's questions quickly compared to her son Rahul's sessions that went on for over 50 hours in five days.
The summons to the Congress chief took political centrestage in Parliament, where opposition leaders raised the issue, and on the streets with party workers staging massive protests.
As parts of central Delhi went into gridlock, Sonia Gandhi reached the probe agency's headquarters on A P J Abdul Kalam Road a little after noon escorted by her Z+ category Central Reserve Police Force (CRPF) security cover.
The Congress president, seen wearing a mask, was accompanied by her children Rahul Gandhi and Priyanka Gandhi Vadra.
Priyanka Gandhi was allowed to stay in the Pravartan Bhawan, the headquarters of the agency, away from the questioning room, so she could be with her mother in case of a health issue and give her medicines.
However, Rahul Gandhi left soon after.
According to sources, she checked on her mother at least twice during the questioning session.
Ahead of Sonia Gandhi's appearance, Delhi Police deployed a huge force, including CRPF and RAF personnel, and barricaded the over one-kilometre stretch between her residence and the ED office.
The Congress slammed the agency's action against its top leadership and termed it 'political vendetta'.
"All Congress MPs and CWC members have courted mass arrest outside our party headquarters in a show of collective solidarity with Sonia Gandhi, a target of 'Vishguru's' political vendetta," said Congress general secretary Ramesh.
His party colleague P Chidambaram said the ED is not higher than the Supreme Court.
"What is that the ED wants to 'investigate' that will not be examined by the SC," he asked.
Outside the Congress office, Sachin Pilot said the ED action was a 'blatant misuse of probe agencies and this has to stop... they cannot muzzle opposition's voice'.
"The case has been built to demoralise the opposition. You can't declare people corrupt because you dislike them."
Other Opposition leaders voiced their protest too.
Leaders of 13 political parties, including the Dravida Munnetra Kazhagam, the Shiv Sena, the Rashtriya Janata Dal and the Left, met at Parliament House and issued a statement accusing the government of unleashing a 'relentless campaign of vendetta against its political opponents and critics through the mischievous misuse of investigative agencies'.
'Prominent leaders of many political parties have been deliberately targeted and subjected to harassment in an unprecedented manner,' the leaders said.
The Opposition's presidential candidate Yashwant Sinha said he strongly condemned the ED's attitude to humiliate political leaders.
'The officers of ED should have gone to her residence even if they had questions to ask of Sonia Gandhi,' he tweeted.
'Yet again the Extended Department (ED) of BJP is insulating the party from people's anger towards price rise, joblessness and inflation. By repeatedly calling opposition leaders with zero evidence against them is deliberate political vendetta carried out on behalf of the BJP,' said Shiv Sena leader Priyanka Chaturvedi.
The issue echoed in Parliament as well where the Congress and other Opposition parties sought to raise the issue.
With tempers running high, Union minister Pralhad Joshi asked whether the Opposition party believes everyone is equal before the law or not.
'Is she some 'super human' because she is the Congress president?' he asked.
The Congress chief had been summoned twice earlier but sought an exemption on grounds of Covid.
Her statement was recorded by the agency under criminal sections of the Prevention of Money Laundering Act.
The probe relates to alleged financial irregularities in the Congress-promoted Young Indian Private Limited, which owns the National Herald newspaper.
The move to question the Gandhis was initiated after the ED late last year registered a fresh case under criminal provisions of the PMLA.
This was after a trial court here took cognisance of an Income Tax department probe against Young Indian based on a private criminal complaint by BJP MP Subramanian Swamy in 2013.
Sonia and Rahul Gandhi are among the promoters and majority shareholders of Young Indian.
Like her son, the Congress president too has 38 per cent shareholding.
Swamy had accused the Gandhis and others of conspiring to cheat and misappropriate funds, with Young India paying only Rs 50 lakh to obtain the right to recover Rs 90.25 crore that AJL owed to the Congress.
In February last year, the Delhi high court issued a notice to the Gandhis for their response on Swamy's plea.
Congress leaders Mallikarjun Kharge and Pawan Bansal were questioned by the ED in the case in April.
The Congress has maintained that there has been no wrongdoing and Young Indian is a 'not-for-profit' company established under section 25 of the Companies Act and hence there can be no question of money laundering.
It is understood that Rahul Gandhi, during his deposition before the ED, stuck to the position that there was no personal acquisition of assets by himself or his family.
According to the ED, assets worth about Rs 800 crore are 'owned' by the AJL and it wants to know from the Gandhis how a not-for-profit company like Young Indian was undertaking commercial activities of renting out its land and building assets.