France and Germany refused US requests to immediately promise extra combat troops for Afghanistan, frustrating President Barack Obama's hopes that more allies would bolster his troop surge.

Britain has already offered an extra 500 troops and Italy has said it will send an unspecified number, while Poland is considering deploying several hundred more soldiers.

US officials say Obama is about to announce a surge of 30,000 troops and British Prime Minister Gordon Brown this week predicted other nations would provide another 10,000.

French President Nicolas Sarkozy's special envoy to the region said late Tuesday France will not deploy extra combat troops to Afghanistan but may send more military trainers for Afghan forces.

"Today, we're ruling out sending ground combat forces," said Thierry Mariani. "We could send extra troops to train the Afghan police and army.... Our extra effort could take several forms."

Le Monde reported that Obama was seeking 1,500 extra French troops for Afghanistan, on top of the 3,400 already there. Mariani confirmed that 1,500 "is one of the numbers that is being put about" but stressed Paris "would take several weeks to give its response."

German Chancellor Angela Merkel said her country would wait until after the London conference on Afghanistan on January 28.

"We are expecting requests from the United States but we will not take a decision in the coming days, we will do so after the conference on Afghanistan," Merkel said after talks in Berlin with Pakistani Prime Minister Yousuf Raza Gilani.

"After this conference on Afghanistan, Germany will decide whether or not it will make fresh efforts, and if so, what efforts," Merkel said, adding that security in Afghanistan would not be solved by military means alone.

Germany has around 4,300 troops in northern Afghanistan, the third largest contributor to a 100,000-strong international force after the United States and Britain, whose extra 500 troops will take it past 10,000 in the war.

Brown set three conditions for Britain sending extra troops to Afghanistan.

These were that the Afghan government show a commitment to providing police and soldiers who can be trained to engage in combat; that British troops are properly equipped and that other NATO countries also boost force levels.

The conditions have now all been met, the prime minister said this week in announcing the reinforcements, saying that eight NATO countries had already made offers of additional troops and others were likely to follow.

Polish Prime Minister Donald Tusk said after a telephone call from Obama that Poland could beef up its contingent of 2,000 troops in Afghanistan by several hundred.

"According to President Obama, a bigger engagement (now) could allow for starting to withdraw the forces in 18 to 24 months from now at the latest," Tusk said in a television interview Tuesday evening.

He added that no decision has been made yet but he has asked Poland's defence minister to prepare a report on how many soldiers would be needed to make the Polish contingent in Afghanistan more effective.

Australian Prime Minister Kevin Rudd pledged Monday to send more police trainers and civilian aid experts to Afghanistan, saying his country was in it "for the long haul."

But Rudd, who met in Washington this week with Obama, did not offer more troops beyond the 1,550 that Australia has already committed.