U.S.-based investment firm Royalty Pharma is unable to go ahead with its hostile $6.4 billion bid for Irish drug firm Elan for now, following a New York court ruling.

Royalty increased its cash offer two weeks ago but Elan, which has rejected Royalty's advances, was granted a temporary restraining order late on Monday blocking Royalty from "consummating or closing" its tender offer.

Elan also won temporary relief from Ireland's High Court on Monday but that lapsed 24 hours later when Royalty agreed not to send further documentation to Elan shareholders until Ireland's takeover body rules on complaints made against its bid.

In its case presented to the Manhattan District Court, Elan said Royalty's disclosures in its increased bid were "materially inadequate" and denied Elan shareholders the opportunity to properly evaluate the offer.

U.S. District Judge William Pauley scheduled a hearing for June 11 when he will decide whether or not to grant a preliminary injunction against Royalty.

Elan said that by reducing the acceptance bar for the bid to 50 percent plus one share from 90 percent, Royalty raised the prospect of taking control of Elan but being restricted under law from delisting it, as its original bid stated.

This could leave nearly half of Elan's shareholders as minority holders in a company controlled by Royalty Pharma but with no clear idea of what the U.S. firm's plans are, Elan said.

"Because of Royalty Pharma's failure to disclose all material information as required by law, Elan's shareholders lack clear and accurate information about Royalty Pharma's intentions," Elan said in its complaint.

"The effect of this uncertainty is to coerce Elan's shareholders to accept Royalty Pharma's inadequate offering price rather than wait to determine the undisclosed consequences of Royalty Pharma taking control of Elan."

Elan said its complaint in the Irish court referred to a proxy statement, filed by Royalty with the U.S. Securities and Exchange Commission last week, which Elan argued had failed to meet several material disclosure requirements under Irish takeover laws.

The matter was adjourned at the court until early on Tuesday when lawyers for Royalty said it had agreed to a request from the Irish Takeover Panel not to send any more copies of the proxy statement to Elan shareholders until the complaints were dealt with.

The panel is due to meet later on Tuesday to discuss the issues raised by Elan, the court heard.

However, in a blow to Elan's hopes of convincing shareholders to reject Royalty's $12.50 per share offer, proxy advisory firm Institutional Shareholder Services (ISS) recommended on Monday that Elan's shareholders reject a series of planned transactions at a meeting due to be held on June 17.

Royalty has made its offer conditional on Elan's shareholders rejecting a $1 billion royalties deal with U.S. company Theravance and a smaller transaction to take over two privately owned drug companies.

Many institutional investors, such as mutual funds, rely on ISS to decide on how to vote in these situations. Elan said last week that there were different opinions among shareholders on the Theravance deal.

(Additional reporting by Abhishek Takle in Bangalore and Nate Raymond and Jessica Toonkel in New York; Editing by Chris Gallagher and Erica Billingham)