* Pompeo says US weighing increase in troops in Poland
* Poland signs deal for artillery rocket system
* Warsaw jittery over Russian assertiveness in east Europe (Adds Pompeo, background)
By Lesley Wroughton and Joanna Plucinska
WARSAW, Feb 13 (Reuters) - The United States is in talks with Poland over Warsaw's request for more American troops on its soil, but no decision has been taken so far, U.S. officials said on Wednesday, as Washington weighs potential military threats from Russia.
Poland asked President Donald Trump last year for a permanent base to complement U.S. troops already present in Poland as part of a rotating NATO deployment in eastern Europe.
"We are taking a look at it and I don't know the ultimate decision we'll make," U.S. Secretary of State Pompeo told reporters during a visit to the Orzysz military base in northeastern Poland, part of his tour of central Europe to bolster U.S. diplomatic engagement in the region.
"But we will make sure we have not only the right number of troops but the right mix of folks out here to do the work that Europe needs and NATO needs and that America needs," he said.
Set up in 2017, the Orzysz base is located about 57 km (35 miles) south of Russia’s Baltic Sea enclave of Kaliningrad, where Moscow has stationed nuclear-capable missiles and an S-400 air missile defence system.
Earlier on Wednesday, the Financial Times quoted the U.S. ambassador to Poland, Georgette Mosbacher, as saying the troop numbers would be raised.
Asked whether the increase would run into the hundreds or thousands, Mosbacher was quoted by the newspaper as saying: "It will be significant. It passes the hundred mark, the hundreds mark."
However, the Pentagon said it was too early to say.
"Any speculation on troop increases or agreements at this point is unfounded," Eric Pahon said in a statement. "No agreements have been reached. We are continuing discussions and will announce the results of our talks at the appropriate time."
The number of U.S. troops in Poland is capped at 4,500 but it fluctuates as formations rotate.
Poland, alarmed by Russia's assertiveness on NATO's eastern flank, has lobbied hard for the stationing of NATO troops on its soil, especially since Moscow’s annexation of Crimea in 2014.
Addressing troops at Orzysz - mostly from the United States but also from other NATO members such as Croatia, Romania and Britain - Pompeo said the alliance needed to counter Moscow.
"As we enter the fifth year of (Russian President) Vladimir Putin's war on Ukraine — a war he launched on European soil — we take seriously those concerns that Russia may one day try to open a front along the line right here," Pompeo said.
In Warsaw, Polish Defence Minister Mariusz Blaszczak signed a deal to purchase 20 High Mobility Artillery Rocket System (HIMARS) from Lockheed Martin, in a ceremony at a Warsaw airbase attended by U.S. Vice President Mike Pence.
Pence is in Warsaw to lead the U.S. delegation at a conference of foreign ministers on Middle East issues, where Washington aims to ratchet up pressure on Iran..
Poland's conservative government hopes to bolster ties with the Trump administration, as it faces mounting isolation in the European Union over its democratic record. It agrees with Trump on issues such as migration, climate change and coal mining.
Trump came to Warsaw in 2017 as part of his second trip to Europe as president, in a major diplomatic coup for the Law and Justice government, which has been in power since 2015. (additional reporting by Idrees Ali in Brussels, Alan Charlish, Pawel Florkiewicz and Marcin Goclowski in Warsaw; Writing by Justyna Pawlak; Editing by Hugh Lawson and Gareth Jones)