SIOUX CITY, Iowa -- Fertilizer company Terra Industries Inc. on Wednesday rejected rival CF Industries' latest unsolicited takeover offer, saying the $4.1 billion bid was still too low.

Terra's said its board of directors unanimously rejected the latest offer, calling it "inadequate, opportunistic and not in the best interests of Terra and its shareholders."

Earlier this week, CF Industries Holdings Inc. -- which has pursued Terra since January -- raised its offer by adding cash to the bid. It said the new bid was worth $40.61 per share, a 5 percent premium on CF's previous all-stock offer.

In response to Terra's rejection of the offer, CF said it "is confident" that Terra stockholders will show their support for the bid by voting for three of CF's nominees for Terra's board. Since October, CF has urged Terra shareholders to vote for its nominees. The voting will conclude at Terra's annual meeting Nov. 20.

Terra has repeatedly rejected CF's buyout offers.

Shares of Terra rose $1.18, or 3.4 percent, to $36.06 in morning trading Wednesday. CF shares rose 13 cents to $85.56 in morning trading.

Meanwhile, CF Industries, based in Deerfield, has been resisting offers by Canadian rival Agrium Inc., which has been trying to take over CF since February.