Paki stan has imposed new travel restrictions on US diplomats living in the country, a source told AFP Sunday, in the latest sign of worsening ties since the killing of Osama bin Laden. A letter sent to the US embassy in Islamabad increased limitations on when and how diplomats can move outside the capital, the diplomatic source said, without giving further details. "We are working with the Pakistani government to resolve the issue," US embassy spokesman Alberto Rodriguez said. Pakistan's foreign ministry said that "no US-specific restrictions have been applied" on diplomatic travel, but added it was "having a constructive engagement with the US Embassy in Islamabad in this regard". "There are general guidelines regarding travel of Pakistan-based diplomats, designed only to ensure their safety and security, which have existed for a long time," it added in a statement. Relations between the US and Pakistan have been under strain in the wake of the raid that killed bin Laden. United State President Barack Obama's administration recently suspended about a third of its $2.7 billion annual defence aid to Pakistan, but assured Islamabad it was committed to a $7.5 billion civilian assistance package approved in 2009.