(CNN) -- Pirates who seized a Ukrainian vessel loaded with tanks and weapons off the African coast have lowered their ransom demand to $5 million.

The pirates initially demanded $35 million and no military action, said Andrew Mwangura of the Kenya Seafarers Association. They decreased their demands for several reasons, Mwangura said.

Those reasons include that the crew is from eastern Europe and not the United States, the weapons the ship carries are secondhand, and there is no way to unload the tanks without coming onto land, he said.

The vessel Faina, flying a Belize flag, was headed to the Kenyan port of Mombasa after departing Nikolayev, Ukraine, according to Lt. Col. Konstantin Sadilov, spokesman for the Ukrainian defense ministry. He said it was seized by pirates Thursday not far from its destination.

According to the defense ministry, the ship was carrying 33 Soviet-made T-72 tanks, tank artillery shells, grenade launchers and small arms.

The weapons were sold to Kenya by the Ukraine, said Ukraine Defense Minister Yuri Yekhanurov, according to the Interfax-Ukraine news agency. He said that the entire shipment was contracted and carried out by Ukrspetzexport, Ukraine's state arms exports monopoly, and that it would know better exactly what was on board.

The ship deliberately took a route far from the coast of Somalia, where pirates are known to operate, in an attempt to avoid them, the minister said.

The Kiev-based source told Interfax on Saturday that radio contact was made with the ship's captain, who reported that the crew has come down with malaria. However, the source said the claim might have been an attempt to hasten negotiations.

Ukraine's anti-terrorist center in its capital, Kiev, is analyzing the situation and consulting with military and security experts, Sadilov told CNN. Ukrainian diplomats are also working in Kenya to resolve the situation, he said.

The Pentagon said U.S. naval ships in the area are "monitoring the situation."

"I think we're looking at the full range of options here," Pentagon spokesman Bryan Whitman said, because the United States does not want the pirates to dock the ship in Somalia and offload the weapons.

The ship's crew consists of 17 Ukrainians, three Russians and a Latvian.

U.S. officials said the ship reported being surrounded by three small boats of pirates while sailing 250 miles off the coast of Somalia.

The Russian patrol ship Neustrashimy, which left Wednesday for the coast off Somalia, may help crack down on pirates, a source in the Russian Baltic Fleet headquarters told Interfax-AVN on Friday.

And the Russian Navy's commander, Adm. Vladimir Vysotsky, told Interfax that Russia plans to send combat ships to the Somali coast to fight piracy.

"We have such plans for the near future," he said. "However, Russian ships will not be involved in any international operations. They will do this job on their own."

U.S. officials, meanwhile, said they are urging all commercial shippers to carry security personnel on their decks when sailing near Somalia. Earlier this week, a U.S. Navy warship fired warning shots at a small boat that got too close to it, fearing a possible attack.

Meanwhile, Mwangura said an Egyptian ship seized by pirates has been released, and a Japanese ship was released after a $2 million ransom was paid.

In addition, a Greek ship was seized by pirates Friday, he said. The ship has a Romanian crew and was heading from Europe to the Middle East.

CNN's Maxim Tkachenko in Moscow and Barbara Starr in Washington contributed to this report.

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