Pentagon officials often say defense cooperation between South Korea and Japan shouldn't be affected by often prickly political and diplomatic ties between the two neighboring nations.

   But they were guarded, if not speechless, when South Korean peacekeeping troops in South Sudan returned 10,000 rounds of rifle ammunition to Japan last week.

   "We don't have anything on that issue," Maj. Robert Firman, a Pentagon spokesman handling Africa affairs, said.

   Asked again via email, he replied, "Still nothing on this."

   South Korea's return of the ammo, less than three weeks after receiving it, was expected following news reports on Seoul's decision in advance.

  Many view the case as demonstrating the difficulty of military partnerships between Washington's key regional allies embroiled in longstanding historical disputes.

   The 280-member South Korean contingent, mostly composed of engineers and medics, has been stationed in the town of Bor, South Sudan, where security conditions have continued to worsen.

   Amid troubles in getting supplies from their homeland, the South Korean force asked nearby Japanese troops in South Sudan through a U.N. mission there to lend them ammunition.

   Japan's Shinzo Abe administration immediately spoke up about Seoul's request, triggering criticism that it is using the emergency faced by Korean soldiers for political purposes.

   A Japanese reporter working in Washington even admitted that there was "excessive coverage" in Japan of South Korea's ammo supply request.

   Prime Minister Abe's visit to the controversial Yasukuni war shine on Dec. 26 has fueled anger among Koreans and suspicion that the conservative leader's intention behind his initiative to expand the role of Japan's Self-Defense Forces outside the country. The shrine honors around 2.5 million war dead, including 14 Class A war criminals.

   The U.S. government also condemned Abe's move. Still, it does not want such political disputes to hamper defense cooperation necessary for dealing with North Korea, and other regional and global security threats.

   "There's a political and historical piece of this. Those are important issues. But that's kind of a State Department, White House, Blue House, Prime Minister's Office to work out," a senior Pentagon official said earlier. "The security baseline is something that we need to keep going even when times are tough on the political side."

   Max Fisher, the Washington Post's foreign affairs blogger, also pointed out Seoul and Tokyo are "terrible" at cooperating with each other.

   "Part of that has to do with rising nationalism in both countries, which can make cooperation with any foreign country difficult," he wrote in his column.

   Above all, he added, "It has to do mainly with their shared history: Japan brutally colonized Korea in the first half of the 20th century, and then spent the second half becoming decreasingly apologetic, with senior Japanese politicians now treating that dark history as a source of national pride."

   He also accused South Korean politicians of "playing up disputes and taking the bait at every provocation."  (Yonhap News)