CALGARY -- The war of words is intensifying between oilsands giant Suncor Energy and its reluctant takeover target, Canadian Oil Sands.

In an open letter issued today, Suncor tells COS shareholders hope is not a strategy when it comes to weathering the downturn in crude prices.

The leadership of COS has urged its shareholders to do nothing, accusing Suncor of being opportunistic and exploiting inside information it has about an oilsands project they jointly own.

Both companies are partners in the Syncrude oilsands development north of Fort McMurray, Alta. -- COS the largest owner with 37 per cent and Suncor with 12 per cent.

Suncor says COS has consistently over-promised and under-delivered when it comes to performance at Syncrude, which has faced a litany of production issues over the years.

Suncor has shown no signs that it's willing to sweeten its all-stock bid -- noting the offer is worth more now than when it was first announced on Oct. 5 because its share price has risen.

It now says the offer is worth $4.7 billion --around $400 million more than when it first launched its hostile bid. The offer would also see Suncor (TSX:COS) taking on $2.2 billion in debt COS had as of Sept. 30, bringing the deal's total price tag to $6.9 billion.

"We don't think hope is an appropriate strategy for Canadian Oil Sands," Suncor CEO Steve Williams wrote to COS shareholders.

"Why? While no one has a crystal ball when it comes to oil prices, the current market outlook doesn't see oil prices getting back to US$60 per barrel until at least 2020."

He also accused COS (TSX:COS) leadership of "misleading spin" about challenges the company faces.

Meanwhile, in a notice on its website, COS says Suncor is paying brokers to get shareholders to tender their shares to the bid.

"Knowing the weakness of their bid, they feel it is necessary to pay brokers and incentivize them to encourage clients to tender their shares," the company said.

"How much are they paying? If you have at least 300 shares, Suncor may be paying your broker a fee of $0.05 per share with a minimum fee of $75.00 and a maximum fee of $1,500. That money does not go to COS shareholders, it goes to their brokers.

"We don't think that's right. We think our shareholders should decide for themselves, free from the influence of brokers being financially compensated to do Suncor's work for them."