(Adds bond prices, updates share price rise) BUENOS AIRES, Feb 8 (Reuters) - Argentine state energy company YPF saw its shares and bond prices rocket on Monday after it won the support of a key creditor group with a last-ditch improvement to the terms of its $6.2 billion debt restructuring. YPF shares were up more than 7% after it sweetened its offer late on Sunday, drawing support from the major Ad Hoc creditor group, which claims to hold about 45% of a bond maturing in March and which had publicly rejected an earlier offer. That breakthrough could help clear the way for the company to complete the restructuring amid a wider economic crisis in the South American country. YPF has been hard hit by the coronavirus pandemic and depressed demand. “With this latest modification, the company expects to successfully conclude its debt refinancing process, adding a greater participation in the offer from all bondholders eligible to participate in the exchange,” a source familiar with the negotiations said on condition of anonymity. “This will result in a greater release of funds for investment activities that allow a return to the growth path in oil and gas production.” YPF, which is spearheading development of the South American nation"s huge Vaca Muerta shale fields, said in a statement here late on Sunday it would offer holders of its 2021 bonds a larger cash payout and extend the time for creditors to accept the offer until Feb. 10. In a statement on Monday, the Ad Hoc group said it accepted the amended offer and that “members holding 2021 Notes will be submitting proxies or tendering their 2021 Notes in the Fourth Amended Exchange Offer on its current terms.” Prices of most of the seven series of bonds involved in the restructuring rose sharply on Monday, with the 2027 notes up almost 7%. YPF, which faces a $413 million payment in March on the 2021 bond, needs to swap some 60% of the total bonds in order to get dollars from the central bank, which has toughened rules to protect declining international reserves. Argentina imposed tough capital controls in late 2019 and pushed firms to restructure foreign debt. YPF said in its statement that its previous offer, which expired last Friday, had received the acceptance of between 14.18% of holders of the key 2021 bonds and 42% from holders of its 2024 notes. The source said the overall acceptance across all the bond series was around 30%. (Reporting by Eliana Raszewski in Buenos Aires and Rama Venkat in Bengaluru; Writing by Adam Jourdan; Editing by Shounak Dasgupta, Kirsten Donovan and Paul Simao)