The Philippines said Friday a deal to allow a greater US military presence on its territory could be signed next month, in a timely defence boost amid a worsening territorial row with China.

There was optimism the pact could be secured ahead of US President Barack Obama's April visit to Manila after the two sides agreed on a contentious issue that would see US forces build "structures" on their hosts military bases, Filipino officials said.

"Discussions in the sixth round were substantive and productive, and significant progress was made," Philippine Defence Undersecretary Pio Batino told reporters in Manila following the latest round of talks in Washington last week.

Fellow negotiators said: "If the negotiations are successfully concluded and that happens before the arrival of President Obama, then we will be happy of course".

However, the officials declined to set an April deadline, citing the need to ensure the language was in line with Philippine laws and yielded the maximum benefits for the hosts.

Washington has said Obama will visit the Philippines in April as part of a four-nation tour of East Asia.

The Philippine government sees hosting more US forces as an important part of its strategy to counter an increasingly assertive China in an escalating dispute over rival claims to the South China Sea.

With its military capabilities dwarfed by China's the Philippines has been looking for more diplomatic and military support from the United States, its former colonial ruler and longtime ally.

A decades-long dispute over rival claims to parts of the South China Sea has sharply worsened over the past two years, with the Philippines accusing China of bullying and violating international laws.

Among the recent flare-ups, Manila accused the Chinese coastguard of firing a water cannon on January 27 at two Filipino fishing boats near a shoal that is within the Philippine exclusive economic zone.

The Philippines then said Chinese ships blocked Filipino vessels from bringing food to Filipino marines on another shoal within its territory.

Both outcrops lie many hundreds of kilometres away from the nearest Chinese landmass, but China claims most of the sea, even waters approaching the coasts of its neighbours.

American forces were forced to pull out of major military bases in the Philippines in 1992, ending nearly a century of military presence, amid a rental dispute and rising anti-American sentiment.

However since 2002 several hundred Special Forces troops on short term deployments have training Filipino counterparts who are fighting Islamic militants in the south.