(For more market insights, including options activity, click on ; for the Day Ahead newsletter link.reuters.com/mex49s; for the Morning News Call newsletter, link.reuters.com/nex49s) U.S. stocks fell at the open on Monday on concern China's economy is continuing to lose momentum and as pro-Russian separatists ambushed Ukrainia forces, escalating a conflict that has kept global markets on tenterhooks recently. The Dow Jones industrial average was down 0.57 percent at 16,418.94 and the S&P 500 was down 0.43 percent at 1,873.09.
** HYPERDYNAMICS CORP, $2.52, +69.13 pct
The oil and gas company said its project partner Tullow Oil had lifted the force majeure declared on its offshore exploration block in Guinea.
Hyperdynamics said it was trying to satisfy the conditions necessary to resume production, including a clarification that a U.S. regulatory investigation of the company would not hurt Tullow's operations under the production sharing contract.
** TWITTER INC, $38.89, -0.33 pct
The six-month "lockup" - the period after the initial public offering during which early investors are barred from selling their shares - ends on Monday. Restrictions on about 470 million shares will be removed. The expiration of the lockup period could put additional pressure on the stock.
According to an article in the May 5 edition of Barron's, Twitter still looks overpriced even after a 47 percent drop from its late December high of $74.
** PFIZER INC, $30.08, -2.18 pct
The company reported revenue well below Wall Street expectations on falling sales of generic medicines, underscoring its interest in pursuing a $106 billion bid for rival AstraZeneca to promote new business growth.
** JPMORGAN CHASE & CO, $54.03, -2.79 pct
The investment bank expects second-quarter revenue from bond and equity trading to decline by about 20 percent from a year earlier, the biggest U.S. bank by assets said on Friday.
Citigroup and Morgan Stanley cut their price target on the company's stock.
** B/E AEROSPACE, $98.705, +10.95 pct
The company, a $9 billion maker of aircraft cabin interior products, said on Sunday it was exploring strategic alternatives including a possible sale, merger or spin off of the company or selected businesses.
German aircraft seating maker Recaro is looking into the news, an executive said on Monday.
** NORDION INC, $12.35, +6.65 pct
Sterigenics, a sterilization services provider owned by private equity firm GTCR LLC, raised its buyout offer for Nordion to $758 million from $727 million on Monday, after the Canadian medical isotope supplier received a rival bid from an unnamed buyer.
** COCA-COLA CO, $40.69, -0.63 pct
Berkshire Hathaway Inc Chairman and Chief Executive Officer Warren Buffett said on Monday he had no desire to "go to war" with Coca-Cola and that U.S. companies were doing well under the current tax code.
** TARGET CORP, $60.41, -2.58 pct
The company's Chief Executive and Chairman Gregg Steinhafel is leaving in the wake of the devastating data breach late last year that hurt profits, shook customer confidence in the No. 3 U.S. retailer and prompted congressional hearings.
** BROADSOFT INC, $19.275, -22.90 pct
The company, which provides internet-based communications services to telecom companies, forecast second-quarter profit and revenue below analysts' estimates. It also reported lower-than-expected first-quarter results on Monday.
** ORBITZ WORLDWIDE INC, $7.33, -1.21 pct
The online travel agency on Monday reported higher-than-expected first quarter revenue and forecast revenue for the current period that topped current analysts estimates.
** GENERAL ELECTRIC CO, $26.51, -0.64 pct
General Electric made tender offers to buy shares worth up to $389 million in two of Alstom SA's India units to comply with local rules, following its $16.9 billion bid to buy the French group's energy unit.
** GOLDMAN SACHS GROUP INC, $155.53, -2.11 pct
A major proxy advisory firm recommended shareholders vote against Goldman Sachs executive compensation plan and added that Morgan Stanley was also paying its top staff too much.
** ARIAD PHARMACEUTICALS INC, $7.54, +4.29 pct
Jefferies & Co analyst Eun Yang on Friday raised her rating on the company's stock to "buy" from "hold", saying that a survey of doctors showed that their use of the company's leukemia drug was minimally impacted by its temporary suspension from the market and its restriction to a smaller group of patients.
Sales of the drug, Iclusig, were suspended in October after it was associated with a higher-than-expected risk of life-threatening blood clots and narrowing of blood vessels, but Ariad resumed selling it with a revised label in January.
Yang also said Jefferies' 50-physician survey indicated that sales of Iclusig were steadily growing after its re-entry in the market, and raised her price target on the Ariad stock to $14 from $8.
** SINA CORP, $47.33, -1.70 pct
Chinese Internet firm Sina said it was fined 5.1 million yuan ($815,038) by Beijing authorities for allowing "unhealthy and indecent content" on its online reading channel and on its main website.
** TYCO INTERNATIONAL, $40.385, -1.04 pct
The security systems maker said its board had approved a proposal to move the company's headquarters to Ireland from Switzerland, citing recent Swiss laws capping executive pay and tightening immigration rules.
** AROTECH CORP, $3.57, +5.93 pct
The defense and security products company said its battery and power systems business had received new orders from military customers for about $5.2 million.
** CAPSTONE TURBINE CORP, $1.715, +1.18 pct
The maker of microturbines said it received multiple orders for two flare reduction projects from distributor Electro Mecanique Industries.
** KING DIGITAL ENTERTAINMENT PLC, $18.47, +5.18 pct
The three lead underwriters of the company's IPO started coverage of the stock with "buy" ratings or the equivalent, two days ahead of the release of the "Candy Crush Saga" game maker's first results as a public company.
** SOTHEBY'S, $43.51, +0.28 pct
Sotheby's said it reached an agreement with Daniel Loeb's Third Point LLC, giving the hedge fund three seats on the auctioneer's board. (Compiled by Natalie Grover; Edited by Maju Samuel)